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Forerunner is the translated name for the ancient race of enlightened beings whose empire encompassed three million fertile worlds in the the Milky way galaxy approximately 100,000 years ago.[1] They were the creators and builders of many significant installations, including the Halo Array, the Ark and Shield Worlds, and many lesser artifacts later found on numerous worlds. All that is known about the Forerunners has been gleaned from these various artifacts. The predecessors of the Forerunner are thought to be another alien race, known as the Precursors. The alien faction known as the Covenant worshiped the Forerunners as gods, deriving much of their technology from Forerunner artifacts found throughout the galaxy, and believing any who mutilated or destroyed these relics to be heretics.[2] The Forerunners themselves were possibly a bipedal species with five-fingered hands[3], but this may have been Cortana's interpretation of the evidence.[4] The Forerunners were a very advanced civilization, coming to power after the disappearance of another race, known to them as the Precursors. They were originally from Ghibalb until it was cleansed of all life when an experiment in stellar engineering accidentally caused several nearby stars to supernova, it is now heavily irradiated and uninhabitable. The Forerunners reached their peak before activating the Halo Array around 100,000 years prior to 2552, in the closing days of the Forerunner-Flood War. Being the only known race ever to achieve Tier 1 technology based on the Technological Achievement Tiers measurement, they were only superseded by the mysterious race of beings called the Precursors at Tier 0, evidence of whom have been found on various planets. The fact that the Halos were scattered around the galaxy also hints at the possibility that the Forerunner Empire covered most, if not all, of the galaxy. During the Forerunners' rule of the galaxy, humanity developed into an advanced space-faring civilization, and attempted to escape Forerunner governance. This rebellion led to a series of wars between the two species. Humanity lost, and as punishment (or to curb their naturally violent nature) the Forerunners dismantled every piece of human civilization and exiled them to their own homeworld. The Librarian was shortly after placed in charge of Earth, and she oversaw humanity's evolution for the next ten thousand years. Later in their history, a Forerunner survey team came into contact with an extragalactic parasite known as the Flood on the planet G 617 g (details of this first contact are unavailable). After this first contact, the Forerunner immediately recognized the great danger that the Flood posed to the entire galaxy and attempted to contain them. However, even they underestimated the potential of the Flood to learn and adapt, believing it to be a non-sentient but highly contagious disease. As such, the attempt to contain the Flood was a failure, as they tried methods more suited to disease control than warfare, trying to contain and quarantine the Flood rather than attack and destroy it outright. They did not start war until it was far too late.[7] When the Forerunners were unable to contain the Flood outbreak, the galaxy entered a state of war. During the 300 years of the conflict, the Forerunner studied the Flood in labs such as the gas mine located in the atmosphere of Threshold, looking for any exploitable weakness. As the Forerunners soon realized that conventional naval tactics were ineffective against the parasite's onslaught, they developed new weapons and tactics to combat the Flood. The Sentinels were deployed as a means of maintaining the Flood through surgical, localized tactics. The Forerunner fleet command even contemplated using naval battle groups to enact premature stellar collapse within compromised planetary systems, causing supernovae to engulf entire worlds.[8]However, as these tactics proved only to slow, but never stop the expansion of the Flood, the Forerunner leadership realized that the only way to stop the Flood was to deprive it of any and all hosts, thus eliminating its potential to grow. Eventually, the Forerunners created the Halo Array, a weapon of last resort designed to starve the Flood to death by killing all sentient life with enough biomass to sustain them.[9] At first, the Forerunners were reluctant to use the Array, believing that they should continue to embrace the Mantle and to protect life rather than to destroy it. This led to great stretches of anguished debate and even civil war, but eventually it was decided that the Array was the only means of successfully stopping the Flood threat. The Gravemind managed to convince a Contender-class AI, 032 Mendicant Bias, to unite with the Flood. Mendicant Bias soon led his massive fleet in an attack on the "Maginot Line", the final barrier between what the Forerunners could protect and what they were forced to abandon to the Flood. At last, the Forerunners exhausted every alternative and activated the Halo array, killing themselves and all sentient life of sufficient biomass in the Milky Way, with the exception of those species safely placed on the Ark. After the Array was fired and the Flood had been eliminated, the species the Forerunners had placed on Installation 00 were returned to their home planets. Whether this was done by remaining Forerunners (it is unclear if any survived) or through automated means is unknown. If some Forerunners remained, then it appears that they chose to leave the galaxy for unknown reasons. It is also possible that they could have left to occupy new galaxies or simply to escape the Halo Array when it fired.

Physiology

The Forerunners were a bipedal species resembling humans in overall shape, though they were larger in stature. Before their first mutation, they were tall and slender, and possessed patches of fine, purple-pink or white fur on the top of their heads, along their nape and shoulder area, as well as the backs of their hands. Their facial features were similar to those of humanity, and they were capable of making analogous expressions, but this changed as they mutated to their higher forms, which characteristically had stiffer facial muscles and a more limited ability to convey emotions. The Forerunners also had a genetic code that was remarkably similar to humans, though they were not known to be genetically related.  Their skin color ranged greatly, including gray, black, blue, pink, or a mixture thereof. The number of fingers Forerunners possessed seems to have varied according to their rate and form; Lifeworkers, for example, were known to have seven fingers, while Bornstellar's later form, based on a mixed pattern, had six fingers.  All Forerunners wore personal body armor which featured many functions, including protection from harm and medical assistance. This armor also eliminated their need to sleep, and made their lifespans basically indefinite; the Librarian, for example, was over eleven thousand years old by 100,000 BCE.

Mutation'

When a Manipular was ready to work within a particular rate, they would undergo an artificially-induced transformation into a more advanced form, which differed depending on the Manipular's chosen caste. Referred to as a "mutation", the transition typically occurred over a long period of time. A typical Forerunner would undergo several mutations over the course of a lifetime, though this was not always the case. Mutations altered Forerunners' abilities and physical shape to suit their class; Warrior-Servants, for example, underwent mutations that made them stronger and more robust. After their first mutation, Forerunners also gained the ability to access the Domain. In emergency circumstances, an operation known as a "brevet mutation" could be performed on a Manipular. This was a mutation that occurred over a much briefer period of time, and was often painful. Rarely, a brevet mutation could fail and result in deformities. The Didact performed a brevet mutation on Bornstellar Makes Eternal Lasting to give him access to the Domain.

Culture

The Forerunner civilization was based around the Mantle, a belief that it was their role to protect all life in the galaxy. They monitored the evolution of other sentient species throughout the galaxy, intervening in ways that ensured their civilizations would follow paths of peace, free of conflict. The Forerunners themselves were a race almost entirely without conflict, and although political disputes were not uncommon, violence or war between Forerunners was almost unheard of. As such, the Warrior-Servants, who conducted most of the Forerunners' military operations, were often looked down upon by the higher rates, as their actions were perceived to be contradictory to their role of preserving life. While they generally strove for peace, when provoked to a war, the Warrior-Servants would carry out the war ruthlessly and thoroughly, as they believed defiance of their rule was equal to showing contempt to the Mantle itself.[28] One example is the human-Forerunner wars, where many humans were executed following their defeat, and all traces of human achievement was erased from the galaxy. The Forerunners had a rigid social structure, where one's position would be determined mainly by their rate, part of a complex system of different social classes mainly based around a particular occupation. Cultural practices and customs varied by rate and position; generally, Forerunner culture was full of formality and ritual, particularly with the Builders. Forerunners placed a great deal of value on family lineage and tradition, and one's rate and social standing were largely hereditary.[29] Despite their lack of need to sleep, Forerunners had certain moments where each member of a household would retreat for several hours of individual meditation. These moments were typically arranged according to the local day-night cycle, and were sacrosanct in traditional Builder families. During this time, the activities on an entire planet would slow down, including traffic and even the operations of ancillas. Forerunners did not eat meat, as the Mantle forbade "the eating of the flesh of unfortunates".[31] Some Forerunners rejected their advanced technology, including personal armor, and adopted a more austere and primitive lifestyle in seclusion from the rest of Forerunner society. One such community existed on Seaward, which would incidentally become the first planet in the Forerunner ecumene to be overrun by the Flood

The Mantle[1] was a Forerunner philosophy. While no precise definition of it exists, it is heavily implied that it was the source of both the Forerunners' "authority" and their apparent duty to preserve the galaxy's biological diversity. Bridging the social strata between an interstellar Marshall Plan and a religious, but benevolent, stewardship, the Forerunners took responsibility for the protection and cultivation of the species and planetary systems within their domain.[2] Forerunner mythology held that the Mantle was passed down to them by an even earlier and more advanced race, the Precursors; to what extent this was true, or even whether or not it was a common belief, remains unknown. The Forerunners believed themselves to be only a passing stage in the universe's Living Time, and that better civilizations would come after them. This is also why they chose to use the name "Forerunner" to refer to themselves.[3] Regardless of its origin, the Forerunners seem to have handed their Mantle down to humanity; it may play a significant part in humanity's Reclaimer status. Some Forerunners doubted the purpose and validity of the Mantle, dismissing it as superstition and fairy tales. The Librarian, in particular, had such doubts, and even went so far as to hold it responsible for the downfall of the Forerunners at the hands of the Flood. The then-rampant AI Mendicant Bias believed that the Forerunners used the Mantle to obstruct any change, even that which might eventually be beneficial. Their central government was entirely dictated by the Mantle, as were the religious beliefs of individual Forerunners. However, inspiring peace throughout their domain by minimizing their military capacity and disarming their weapons cache proved to be a costly approach for the Forerunners when the new alien threat emerged. Rather than allowing every species to rise on their own merits, the Forerunners, following their Mantle, gave them no need to do so, serving as protectors against any threats that might have forced technological or cultural progression. An unforeseen side-effect was that only the Forerunners were able to hold their own against the Flood (at least once they rearmed), while their charges were unable to defend themselves; the Forerunners had unintentionally left the galaxy vulnerable to Flood infection. The Twelve Laws of Making and Moving were a central religious text of the Mantle often recited in prayers.[3] A Master of the Mantle was an individual, likely a religious official, whose duties included securing a Forerunner's physical remains into a Durance after an immolation ceremony.

The Ecumene is the Forerunner empire which existed over 100 thousand years ago. It stretched across the galaxy and consisted of three million planets.[1] The political center of this empire was known as the Capital, a massive structure containing multiple cities.

The Capital was the political center of the Forerunner Ecumene. It was a massive structure, exceeding the scale of even the Halo Installations. The Capital was composed of a series of perfectly circular "platforms" arranged in a spiral along a central rod. These platforms decreased in size toward either end of the rod, with the widest central one being approximately 100,000 kilometers in diameter. Each platform was covered with a "city" of structures and buildings.

The Maginot Line,[1] otherwise known as the Maginot Sphere, was a Forerunner defensive line that protected the Forerunner inner colonies. It divided what the Forerunners were able to protect from what they had to leave to the Flood. Its precise location is unknown; however, Earth was most likely not inside it and neither were most of the worlds the Librarian visited in her duties.[1] It was heavily damaged when the Flood made a massive attack on it, led and commanded by the rampant Forerunner AI Mendicant Bias. It was the primary line of defense holding the Flood back. It is assumed that it was broken before the first firing of the Halo Array. Although it was a defense against the Flood, it cannot be assumed that the Flood conquered all worlds that were outside of the Sphere, as Earth (which was suspected to lie outside of the sphere) was presumably not infected, because the Librarian was on it, marveling over its beauty before the Array fired. It can be assumed that for a long time, the Didact worked in the Maginot sphere, frequently sending transmissions from it to the Librarian asking her to retreat behind it to where the Didact said their Fleets could protect the Librarian. The Maginot Sphere may have been a physical object, (an energy barrier or a defensive line of some sort) as a Keyship was needed to enter it. It may also be a hypothetical line, not a physical object, used to mark what could and could not be saved, and the fleets guarding it would not permit anyone or anything to pass unless it was in a Keyship.

Funerary rites'

When a Forerunner died (usually by accident or, on rare occasions, during war) elaborate ceremonies would be enacted before their remains were disposed of in fusion fires associated with the activities of their rates — a melting torch or planet cutter, for example. First, the Forerunner's last memories would be extracted from his armor, which preserved a few hours of the occupant's mental patterns. This reduced splinter of personality would be placed in a time-locked Durance, which has a half-life of more than a million years. The body would then be torched in a solemn ceremony attended only by close relations. A bit of plasma from the immolation was preserved by the appointed Master of the Mantle, who secured it along with the essence in the Durance. The Durance was then given to the closest members of the dead Forerunner’s family, who were charged with making sure that it would never be abused. Families and rates were very protective of such places, and tampering with a family Durance was considered sacrilege.

A Durance was a type of Forerunner memory storage device. Upon the the death of a Forerunner, the individual's last memories and mental patterns were stored inside a Durance. The Durance and a bit of plasma from the immolation of the body were then presented to the closest family members of the deceased.[1] Durances had a half-life of a million years. Their resting places were closely guarded by the family, such that the violation of a Durance was considered sacrilege

Leaders

The Ecumene Council was the main government and lawmaking body of the Forerunner ecumene. It was located at the capital. Lead by the First Councilor and composed of five hundred Councilors from various rates, the Council was supported by a network of ancillas known as the Council metarchy. The Council's dedicated security force was known as Council Security. Councilors typically served for a thousand years and took vows of abstinence and austerity. This was apparent in the general aesthetic associated with the Council; their ships and residential facilities lacked luxury or adornment, yet reflected the Council's status and power.

Faber, more commonly known by his title as the Master Builder, was an immensely powerful Forerunner Builder.[1] He commissioned the construction of the Halo Array, and co-created Mendicant Bias alongside the Didact. Sometime following the end of the Human-Forerunner War, Faber commissioned the creation of the Halos, an array of weapons capable of purging all sentient life from a star system and, if the situation became dire, the entire galaxy. The purpose of this project was two-fold: to be used as a defensive measure against the Flood were they ever to return to the galaxy, and to secure the preeminence of the Builder rate. Despite opposition from the Didact and the Prometheans, who managed to delay the construction of the Halos for thousands of years, the Ecumene Council eventually agreed to Faber's proposal, causing the Didact to go into exile.[2] Under Faber's orders, the father of Bornstellar Makes Eternal Lasting designed the Halo Array, and twelve of the weapons were built by his guild. However, the Librarian and the Lifeworker rate strongly opposed the construction of the Halos, viewing them as contrary to the principles of the Mantle. With the Lifeworkers threatening to go on strike if the weapons were constructed, the Council agreed to the Librarian's demands to provide a workable plan to save sentient life in the galaxy in the event the rings were ever fired. This plan, known as the Conservation Measure, involved giving the Lifeworkers biological preserves for specimens of numerous species on several of the Master Builder's installations, including the Halos and their construction foundries, known as the Arks.[4] After the onset of the Forerunner-Flood war, Faber authorized the use of the Lifeworkers' biological specimens on the Halo installations for experimentation on the Flood in hopes of finding a cure to the parasite.[5] Of particular interest to his researchers were humans, primarily housed on Installation 07, many of whom seemed to exhibit an immunity to the parasite - unaware that this was due to an ongoing strategy on the Flood's part. He authorized that more humans with the Librarian's special geas be brought on the installation from Earth, against the instructions of the Council and the Librarian. Circa 100,043 BCE, Faber, with the Council's authority, tasked Mendicant Bias with conducting the first test of a Halo installation near Charum Hakkor. Installation 07, fired on a system-wide power setting, released an ancient being known as the Primordial; the entity was taken on the installation by Faber's orders afterward. As he did not trust the Lifeworker scientists who at first studied the creature, Faber soon assigned Mendicant Bias to interrogate it.[6] Over the course of the extended conversation, the Primordial managed to encourage the Master Builder to continue the experiments on humans, and eventually convinced Mendicant Bias to turn to rampancy and defect to the Flood. Around 100,000 BCE, he arrived at Janjur Qom to seek information on the Flood from the San 'Shyuum leadership. Their arrival, following the Librarian's indexing of the San 'Shyuum, caused the San 'Shyuum to rebel against the Forerunners. In retaliation, the Master Builder ordered Mendicant Bias to use Installation 07 to sterilize the San 'Shyuum population.[8] During the battle, Faber's forces intercepted the ship carrying Bornstellar and the Didact, who had also come to meet with the San 'Shyuum leadership. He placed the Didact under arrest and sent Bornstellar back to his family.[9] When the Didact later refused to give vital information to the Master Builder, he left him to die in a Flood-infested system, with the rest of the galaxy believing him to be dead.[10] The Didact would continue interfering in his plans, however, as his memories and personality had been transferred to Bornstellar's mind. However, the Master Builder had overestimated his control over his allies. They believed that the Halo Array was intended as a last resort weapon, not to punish uprisings. Many of his closest allies felt he had violated the Mantle for with his actions, and a political revolution occurred, with many Councilors resigning in protest. Meanwhile, many Lifeworkers and Warrior-Servants on Installation 07 violently rebelled against the Master Builder, but this revolt was mostly suppressed by Faber's loyal Builder Security forces.[6] The Builders stripped Faber of his title, and he was put on trial before the Forerunner Council for the unsanctioned use of a Halo and other war crimes.[12] However, the trial was interrupted by Mendicant Bias' assault on the capital.[13] Though Faber's ultimate fate remained unknown, it was assumed that he died somewhere on Installation 07.[14] Despite his high standing in Forerunner society, Faber displayed arrogance and cruelty wholly at odds with the Forerunner ideals of peace and enlightenment. He held utter contempt for less-advanced species, as well as lower-ranking Forerunners. He also was not above using torture against those who crossed him. Regardless of his cruelty, Faber was exceptionally powerful in many ways; in addition to his political power, he was noted as being an individual of "near-infinite complexity and mental resources," equally cunning to the Didact, and possessed immense knowledge of Forerunner politics and technology. Faber appeared to dedicate considerable attention to his personal appearance, making use of perfumes and maintaining an attitude of superiority in all encounters.

The Didact[1] was a Forerunner Promethean who held an extremely high status in the Forerunner society as supreme commander of the entire Forerunner military. He wholeheartedly believed in the "Mantle" the Forerunners held to protect life, and initially opposed the Halo Array as a sin beyond measure. He was also the lover and husband of the Librarian, and the one who eventually activated the Halo Array.[2] The Didact was a Promethean, a member of an extremely powerful class of Warrior-Servant. Following the end of the Human-Forerunner War and the first discovery of the Flood, he advocated a policy of vigilance and research in the event of a Flood resurgence. He also proposed the construction of Shield Worlds across the galaxy, in order to monitor the galaxy for Flood outbreaks and provide military support should they occur. However, a faction of Builders at the time proposed the construction of a series of superweapons to deal with the Flood instead, and they were successful in convincing the Council to sanction their plans. Having lost the political battle, the Didact was stripped of his power and forced into exile. At some point, he entered a state of meditation inside a Cryptum, which somehow ended up in Djamonkin Crater on Earth. Over a thousand years later, he was discovered and awoken by a young Forerunner Manipular, Bornstellar Makes Eternal Lasting, who had come to Earth in search of Precursor relics. During his subsequent travels with Bornstellar, the Didact performed a brevet mutation on him to allow him access to the Domain. Shortly afterward, the Didact transferred all of his memories and knowledge to Bornstellar, essentially merging his personality with the young Forerunner. The Didact was later executed at the hands of the Master Builder, making Bornstellar, for all intents and purposes, the reincarnation of the Didact. He would go on to meet his wife, the Librarian, aboard Installation 00.

The Librarian[1] was a Forerunner Lifeworker, and one of the most powerful and influential Lifeworkers who ever lived.[2] The Librarian was a Lifeshaper, the highest rank a Lifeworker can achieve, and one of only three Forerunners ever to receive the title.[2] Following the Human-Forerunner War, she was permitted by the Forerunner Council to set up a research station on Earth (then known as "Erde-Tyrene"). Over the span of ten thousand years, she helped the human species, which had been devolved to a primitive state following the war, to slowly work toward re-creating a primitive society.[2] The early humans viewed the Librarian with reverence, believing her to watch over all of the humans and come to each one at birth and assign them a purpose. Bornstellar hypothesized that she may have imposed a Geas on certain humans.[3] At some point, the Librarian traveled to Installation 00, where she later met with Bornstellar Makes Eternal Lasting (now in possession of the Didact's memories and personality.)

05-032 Mendicant Bias was a Contender-class Forerunner artificial intelligence. He was the most advanced Forerunner AI at the time of his creation, and was charged with organizing Forerunner defense against the Flood before his defection to the Gravemind, who ultimately caused him to become rampant, and turn against his creators. Mendicant Bias was created by Faber and the Didact following the Human-Forerunner War, after the original Flood attack on the Milky Way had been pushed back by humanity. After the Flood returned, in 100,043 BC Mendicant Bias was tasked with resisting the Flood by studying and exploiting the weaknesses of the first Gravemind. As part of his assignment, he was given control of one of the Halo Installations, and traveled with it on a scheduled testing mission. With the old Council's authority, he tested the weapon at Charum Hakkor on a low power setting. Approximately three years after exiting the Maginot sphere, Mendicant Bias intercepted a communications signal of unknown origin, to which he responded. After a short period of dialogue, he discovered that he was in fact speaking with the Flood Gravemind. He continued communicating with the Gravemind in an effort to find any possible weakness, sending logs of these conversations to his Forerunner masters. After conversing with Mendicant Bias for 43 years, the Gravemind persuaded him to abandon the Forerunners and join the Flood cause, convincing him that the Forerunners were so arrogant and prideful as to deny the next step of evolution: the Flood.[2] The Gravemind insinuated that by clinging to the legend of the Mantle, the Forerunners had doomed the galaxy to eternal stagnation; the only way for the galaxy to progress was for superior beings to "restart" it. These superior beings, unsurprisingly, took the form of Compound Minds such as Gravemind and Mendicant Bias himself. Although the 43-year long conversation logs between Mendicant Bias and the Gravemind were sent back to the Forerunners, they believed that Mendicant would automatically fulfill its objective and destroy the Gravemind, so they did not intervene.[3] Convinced by the Gravemind's arguments, Mendicant Bias intentionally became rampant, developed a hatred for his creators and actively worked toward their destruction.

Offensive Bias is a Contender-class[1] Forerunner Artificial Intelligence that was created to stop the rampant A.I. Mendicant Bias from reaching Installation 00 to stop the Array sequence. Even though Mendicant Bias' Fleet outnumbered Offensive Bias' by 2183:5, Offensive Bias was designed specifically to effectively counter and exploit Mendicant's rampant actions. During the battle, the Halo Array was fired which, aside from killing all sentient life in the galaxy, disabled the percentage of Mendicant's fleet which were biological. After the Halos fired, the advantage turned Offensive Bias's way, outnumbering Mendicant Bias's fleet 6:1. What happened to Offensive Bias after this success is not specified.

Rate System

Forerunner society was divided into a number of different classes known as "rates", each rate specializing in a particular field of work. The Builders, who designed the Forerunners' various megastructures, were the highest rate and wielded the most political power. The second rate were the Miners, who obtained construction materials for the Builders' projects. Below the Miners were the Lifeworkers, who were responsible for medicine and biological research. The Warrior-Servants, the primary fighting force of the ecumene, were the fourth and second lowest rate. The lowest rate were the Engineers, who were tasked with constructing and operating Forerunner structures and machinery, as well as planetary and stellar engineering. The rates, in turn, were divided into smaller units, guilds, Maniples and clans. Adolescent individuals, known as "Manipulars", were not considered to be part of a rate until their mutation into first-form. During special occasions, each rate of Forerunners wore unique ceremonial headgear except for one day of Grand Star Season, when all rates would wear similar headgear.

The Prometheans were the highest and most respected group of Warrior-Servants in the Forerunner ecumene. During and after the Human-Forerunner War, they were led by the Didact. During the Forerunner-Flood war, the Prometheans' main base of operations was the fortress world known as Requiem. Elements of the Prometheans survived the Forerunner-Flood war and the activation of the Halo Array, eventually awakening within Requiem and rising to oppose the UNSC in 2557.

Warrior-Servants or Warriors were the second-lowest rate in Forerunner society. As their name suggests, they were responsible for defense and warfare in the Forerunner ecumene.[1] The Warrior-Servants were presumably all subordinate to the Warrior-Servant Corps.[2] They utilized many different war machines, including war sphinxes. Warrior-Servants were typically more powerfully built and more robust than the other rates such as Builders.[3] The highest and most respected class of Warrior-Servants were known as the Prometheans. While Forerunner society was peaceful by nature, Warrior-Servants were ruthless in executing warfare against enemies of the ecumene, as they believed that defying the Forerunners was to show contempt toward the Mantle itself.[4] Although their services were vital in maintaining galactic harmony, most Forerunners viewed their purpose and practices as being contradictory to the principles of the Mantle. As such, other rates looked down on the Warrior-Servants, who mostly kept to themselves as a result. It was a common policy among Warriors to harvest the memories of their vanquished foes before executing them. The highest class of Warrior-Servants, known as the Prometheans,[7] had once been in high social standing and power, serving in various roles in the Ecumene Council. However, after the conclusion of the Human-Forerunner wars, the Prometheans were opposed to a Builder plan to construct a new superweapon known as the Halo Array. Circa 101,000 BCE, the Prometheans lost this political battle and were removed from the Council,[8] some of them entering self-imposed exile in "Warrior Keeps" known as Cryptums, while others were executed.[9] This also resulted in the entire Warrior-Servant rate being marginalized, with their fleets and armies being systematically disbanded over the course of the next millennium.[8] This would leave the ecumene ill-prepared for the return of the Flood.

The Builders were the highest rate of the Forerunners, considered to be the most powerful in terms of intelligence, wealth, and political power.[1] As their name suggests, the Builders were responsible for designing and constructing the myriad technologically advanced structures and objects seen throughout the Milky Way galaxy, including the Halo Array.[1] The chief of the Builder rate and all its guilds was known as the Master Builder. The Master Builder was often considered the most powerful Forerunner in the ecumene.[2] Builder forms were generally tall and sturdy in build, but more refined and sophisticated in appearance than Warrior-Servants. Builder security was a group of Builders who conducted security and combat matters.

Builder Security was a group of Forerunner Builders who conducted security and combat matters for other Builders. They commonly used Seekers for their operations.

Miners were the second-highest rate in Forerunner society, ranking below Builders but above Lifeworkers. After disobeying his father, Bornstellar Makes Eternal Lasting, a Manipular from a Builder family, was sent to work with the Miners on Edom.

Lifeworkers were the third-highest rate in Forerunner society.[1] They specialized in all living things and medicine, including experimenting with new forms of life. The highest possible rank achievable by a Lifeworker was Lifeshaper. Earth, then called "Erde-Tyrene", was at one point an experimental planet under the care of the Librarian, a Lifeshaper and one of the most powerful Lifeworkers to have ever lived.[2] Lifeworker forms were typically graceful and tall compared to other rates. The Lifeworkers, under the Librarian's control, were responsible for maintaining the ecosystems on Installation 00 and the Halo Array using them to research, store and index species collected from numerous worlds across the galaxy in the Conservation Measure. Lifeworkers appear to prefer to float using parts of their armour, as opposed to walking like most Forerunners. This is seen quite prominently with the Librarian and her Lifeworkers on Installation 07.

Engineers were the lowest rate in Forerunner society, responsible for construction and maintenance of machinery, as well as stellar and planetary engineering. Stellar-class Engineers were referred to as "plasma jockeys" by Builders. Unlike the other rates, Engineers were not represented in the Capital Court.

Plasma Jockey was a colloquial term used by Forerunner Builders to refer to stellar-class Forerunner Engineers. Equipped with third-class ancillas, plasma jockeys were tasked with "taming" young stars for future use.[1] While most plasma jockeys succeeded in their tasks, many simply disappeared after a few hundred years, and no one knew what became of them.

Forerunner technology

The Forerunner's technological achievements were without parallel in the known galaxy. They managed to create solidified surfaces out of light, use Slipspace to teleport between locations almost instantaneously, and create numerous forms of advanced machinery. The Halo Rings themselves, the Micro-Dyson Mark II sphere, which is connected through a portal to the shield world Onyx, and the Ark (Installation 00) are, above all others, the most significant pieces of Forerunner technology. The planet Onyx in particular demonstrates both their ability for engineering on a grand scale, and their near transcendent grasp of Slipspace technology. It is unknown how much of their technology is based on the technology of the Precursors if any. Covenant Luminaries (which are actually recovered Forerunner equipment designed to detect other Forerunner objects) can detect Humans, previously mislabeled as "Forerunner Artifacts", leading to the initial Human-Covenant contact which sparked a seemingly endless war. Ironically, the Covenant worships the Forerunners but fight Humans, who have been confirmed as Reclaimers by the Oracle. Forerunners have the technology to reproduce entire individuals from encoded DNA/RNA/silicon samples in data streams. This was mentioned in the Bestiarum: "DNA/RNA/Silicon samples are encoded in this data stream. Reproduction of individuals for analysis is prohibited by this facility." The Forerunners had the ability to either create artificial stars, or move existing stars across distances of thousands of lightyears, either of which would be a tremendous technological feat. Additionally, they seem to be able to extrude whole stars (and probably the surrounding system as well) into Slipspace. One star was used in the construction of the Shield World, Onyx, while an artificial star, created just for it, orbited Installation 00. The Flood-Controlled Shield World also had a miniaturized artificial star in its center.

The Domain was a Forerunner information sharing network. While its exact nature is unknown, it is known that mature Forerunners were able to connect to the Domain through their armor and that all Forerunner knowledge was accessible through it.

Cryptums, or Warrior Keeps, were powerful objects created by the Prometheans. A Cryptum was a sealed capsule where a Warrior-Servant would enter self-imposed exile, involving a state of meditative hibernation known as "timeless xankara". During this time, the Forerunner would become unaware of the physical world around him, and could remain in a state of suspended animation for thousands of years. Cryptums required an extraordinary amount of force to breach once sealed. They denied access to every species except Forerunners. The nature of a Cryptum was unknown to most Forerunners, including Bornstellar Makes Eternal Lasting. However, he was aware that the violation of a Cryptum invoked dire consequences, one of which was angering the powerful Prometheans.[1] A Cryptum was discovered in Djamonkin Crater by the young Forerunner Bornstellar Makes Eternal Lasting, containing the meditating Didact.

Sentinel launchers, are small armor-covered devices built into the walls of some Forerunner facilities. They have appeared in Halo 2 and Halo 3. When hostile entities, such as Flood, are detected in the immediate area, they open their cover and dispense Sentinels. When a Sentinel is about to be dispensed, the Launcher will make a noise that increases in pitch until the Sentinel is dispensed. Most Sentinels seen being dispensed are the normal silver ones, though a few dispense the gold, shielded Majors. One way to destroy a launcher is to attack it when the armored cover opens to release a Sentinel (an over charged Plasma Pistol shot is a one shot kill and also creates an EMP style effect on nearby shields.) It is also possible to destroy a closed dispenser by sticking a Plasma Grenade on its cover or by hitting it with a melee attack; however, the melee attack will drop your shields, so it's most useful to melee the Launchers when there are no other enemies around. These launchers can only be found on the level Sacred Icon in Halo 2 and only briefly in the Halo 3 levels The Ark and Halo and are allied with the player. They can additionally be seen in diagonal rows along the sides of the support beam of Installation 04 (II)'s Control Room. This has confused a lot of Halo 2 players as on the levels The Arbiter and Oracle there are Sentinels but no Sentinel Launchers. Although some Sentinels could have escaped the destruction of the first Halo, few would have been able to do so. There are an extremely large number of Sentinels on the two levels and too many for the amount that could have escaped Halo's destruction. This would probably mean that they came from a production facility of some sort or are produced on site and are in fact Sentinels that originated from the Gas Mine. The launchers in Halo 3 release Sentinels at a quicker rate than those in Halo 2. Also, the hatch closes right after the Sentinel is released to prevent weapon fire from getting into the launcher. To get around this, just stick it with a grenade or blow it up with a heavier weapon such as a Rocket Launcher.

All Forerunners wore personal body armor through most of their lives. The armor protected its user both physically and medically, granted them immunity to most diseases, and was one of the reasons for their long lifespans. In emergency situations, the armor could suspend its user until they were rescued, and even provide nourishment for a time. Most if not all Forerunner body armor possessed N-barriers, lenses, and "omniscient guides" to protect the user from harm.[1] Mature Forerunners could connect to the Domain through their armor. Forerunner armor suits were also equipped with ancillae, personal artificial intelligence constructs.[2] Armor suits specifically designed for combat were known as Combat Skins. Though the body armor provided the user with certain advantages, it also caused the user to lose sensitivity to the world around them. For example, when Bornstellar Makes Eternal Lasting decided to remove his body armor on Earth, he found himself exceedingly vulnerable; a simple touch from Chakas caused him to react. While wearing the armor, sleep is not required.

N-barriers were a form of Forerunner shielding. They were used in the armor of the inhabitants of Seaward, and were likely in widespread use by the advent of the Forerunner-Flood War.

Artificial intelligence suppressors, or AI suppressors, were pieces of Forerunner technology designed to deactivate ancillas. The suppressors were also able to debrief and transfer all of the targeted ancilla's collected information instantly.

Very little is known about the Forerunner Combat Skin, other than that it was used by combat personnel and was comparable to, but far more advanced than, the UNSC MJOLNIR Powered Assault Armor. It is first mentioned by 343 Guilty Spark as he is leading John-117 through the Library, wondering why he had brought "such ineffective weapons" to combat the Flood. He notes that the MJOLNIR is ill-suited to combating the Flood, and recommends that he upgrade to a Class 12 Combat Skin from the MJOLNIR, which is ranked on the Forerunner classification system as a Class 2. On the other hand, Guilty Spark also notes that the MJOLNIR will serve John well when the Flood begins converting Halo's atmosphere, commenting that he is a "good planner".[2] Upon learning that there was a powered armor system six times more powerful than the MJOLNIR, John expressed enthusiasm at the opportunity to wear one.[3] The Terminals on Installation 00 indicate that other Combat Skin classifications existed, ranging from 1 to 4, and that there were other suits of a similar nature, such as the Battle Harness, with its own classification ranging from 1 to 6, and the Platform Interface Skin. Eventually, all Civilian personnel were required to wear at least a Class 8 Combat Skin unless in core areas, and all Military personnel were required to wear at least a Class 12 Combat Skin.[4] During at least the early years of the Forerunner-Flood War, Forerunner ground troops used Combat Skins that, while certainly powerful, lacked energy shields, leaving their wearers extremely vulnerable to Flood infection. It is likely that, rather than representing the peak performance of the technology, it is indicative that the Forerunners were woefully unprepared for the Flood onslaught, and were initially slow to adapt their equipment and technology to fighting a purely biological foe.[5] During the Battle of Installation 00, Guilty Spark can be heard lamenting that John did not upgrade his Combat Skin. The fact that the Mark VI is more advanced than the Mark V that Guilty Spark had previously encountered and is still classed as a Class 2 may indicate that the Combat Skin class system is based on another factor other than combat performance, or that despite its upgrades it was still inferior to a Class 3 Combat Skin.[6]

A Line Installation is a Forerunner installation with the purpose of containing the Flood. Line installations serve as Flood research facilities, and are designed to target and destroy any Flood-infested ships passing within close range of the installation in Slipspace.[2] These installations are usually located on a satellite of a nearby planet. Each installation has its own Monitor and a control center, as well as a sizable force of Sentinels and Gatherers. At some point during the Human-Covenant War in the late 2552, the Long Time Coming, as well as the Covenant assault carrier Clarity of Faith were shot down by Line Installation 1-4's defenses while in Slipspace.[3] As a result, they both crash-landed on an unidentified moon in Sub-sector 35. Personnel were taken by Gatherers into the main facility of the Installation, for study by the installation's Monitor, 686 Ebullient Prism.[4] During the Battle of Line Installation 1-4, the installation's control center was located and used to shoot down an entire Covenant fleet in Slipspace

A baffler was a type of Forerunner stealth technology that used geometric distortions to hide an object or location. In approximately 100,000 B.C.E., a baffler, by then considered outdated, was used to hide the center of Djamonkin Crater.

A dazzler was a type of Forerunner stealth technology that used "delusions" to hide an object or location. A dazzler may have been used at the Menachite Forerunner complex.

Platform Interface Skin was a piece of equipment issued to Forerunner weapon platform specialists to ensure peak mind-machine synchronization.[1] From this, it can be deduced that platform interface skin uses some kind of neural technology. As of Fleet-wide Memorandum 2/5, all weapon platform specialists were required to wear platform interface skin at all times

Modular Dispersal Technology or "MDT" is the UNSC name for the technology relating to the detachment of modular starship sections while in a vacuum.[1] The technology was first used by the Forerunners during the war against the Flood to break off infected sections of ships while allowing the rest of the ship to continue operating.[1] The Modular Dispersal Technology is equipped to certain Covenant warships for use. It is used by the Covenant to detach damaged, non-critical sections of a ship rather than return to a repair center, or to disperse a part of the ship which could leave any hostiles stranded in space. To do this the ship must detonate charges that would break off that part of the ship. Due to the modular design of Covenant ships, a ship would be able to function even with a large amount of its major sections detached. Afterward, a ship could be easily reassembled at a repair facility.

Forerunner Slipspace pods are somehow connected to slipspace and normal space, the actual bodies contained inside the pods are within slipspace, making them safe from nearly everything. (Nearly means that they might be able to get killed if they are engaged within Slipspace, otherwise, normal space cannot hurt the person inside.) They are visible via an afterimage seen within the pod, essentially a snapshot of the moment they "left" time. Although not technically in our space, those stored "within" the pods may be transported by moving the pods themselves. This method works as the Slipspace generator is located on each pod. If a person comes too close to the pod they will develop nausea, and a feeling of light-headedness due to exposure of an unshielded Slipspace field. Currently, the method of releasing one from these pods is unknown. On the sides of the pods there are Forerunner icons which Dr. Catherine Halsey translated into "That which must be protected...behind the sharpened edge of the shield...beyond the reach of the swords...for the reclaimed".[1] However, Dr. Halsey noted that her translation was off, and agreed with Ash when he suggested that is was instead "Reclaimers", when he brought up about his encounter with an Onyx Sentinel. This was not the first time the word has been misinterpreted this way, as the same mistake was made by the Covenant late in their history, in which the Oracle residing within the Forerunner Dreadnaught noted and corrected as "Reclaimers".

Biotechnology

The Forerunners had the technology to reproduce entire individuals from encoded DNA/RNA/silicon samples in data streams. The Forerunners were also capable of extracting an individual's brain patterns and memories; typically, part of a dead Forerunner's final memories were typically recovered and stored in a container known as a Durance.[  In a mutation, part of the mentor's consciousness would be transfered to the individual being mutated through their genetic imprint. Recovered memories or specific commands could also be coded into a generations-long genetic imprint known as a geas. Memories or messages stored within a geas could be programmed to trigger under specific circumstances

The Huragok are actually not a natural, biological species at all, but rather an artificial life form created by the Forerunners. While they possess no true tissues or organs, their nano-mechanical surrogates so closely mimic their biological analogs that they seem almost indistinguishable to observers.[3] Multiple gas-bladders serve as their method of locomotion, allowing them to float through the air even after their deaths. The bladders also serve as part of their respiratory system; if their gas bladders deflate, they will asphyxiate and die. They have small heads with six dark eyes, and four tentacles that can split into very small, near-microscopic cilia. The Engineers use these cilia to construct, repair, or rebuild nearly anything they can grasp. They can take apart whole vehicles and rearrange their entire structure in a matter of seconds, with the resulting machines still operating at least as well as they did before. They learn at an unprecedented rate, and store that information for future reference if ever they need to repair the same thing twice. They are capable of surviving in at least oxygen and methane-rich environments, though they cannot survive in a vacuum.[11] Huragok are not normally a tactical threat and are hardly ever seen in combat situations. Most UNSC soldiers make a point of avoiding intentionally harming Huragok if possible. Unlike the majority of the Covenant races, they do not regard humans as enemies; during the John-117's assault upon Ascendant Justice, one even aided the SPARTAN-II by repairing the shield generator on his MJOLNIR armor and fixing the SPARTAN's current weapon, a broken Needler.[7] However, Lieutenant Haverson killed the Engineer stating that it had learned all about the MJOLNIR shield technology, which was superior to the Sangheili Personal Energy Shield, and could not be allowed to relay that information. In Halo: Contact Harvest, a Huragok named Lighter Than Some attempted to aid the Humans in an attempt to bring peace; he even made them a peace offering, which, against his wishes, was converted into the Brute Chopper. Huragok "reproduce" by gathering the needed (or available) materials from their surroundings to "build" another Huragok.[12] This new offspring is then filled with a precise mixture of lighter-than-air gasses. The initial buoyancy of the newly born Huragok is what it is named after.[13] Three known Huragok names have been revealed so far. Those who sink are named 'Far Too Heavy'. Those whose buoyancy is almost perfect are named 'Easy to Adjust'. Lastly, those whose gas mixture causes them to exhibit extreme buoyancy are named 'Lighter Than Some'. Up to three Huragok take part in this process, relaying all the information that they have learned to their "offspring". Given sufficient raw materials, a pair of Huragok can produce a unified replica of themselves in approximately 45 minutes; the addition of a third Huragok cuts the time down to thirty minutes.[14] Understandably, it is advantageous to have as many Huragok contribute to this process as possible, raising the "intelligence" of the offspring. When deployed during large-scale archaeological expeditions, Huragok make use of large Recharge Stations, where they rest, repair each other, and share data between forays. Huragok blood is luminescent blue-purple in color, as seen in Halo 3: ODST. Huragok are bioluminescent, and in dark conditions their heads and tentacles emit a bright bluish glow, which seems to pulsate when the Huragok is calm and dim when it is frightened. The cilia on their tentacles give off a pinkish-red light as well. Though the inner workings of an Engineer's internal macroscopic biology remain a mystery, it is known that they are capable of using the gas sacks that keep them afloat for anaerobic respiration. This method is painful, dangerous, and apparently only used as a last resort.[15] In the Halo series, only one usage of the ability has been described: when Lighter Than Some used anaerobic respiration to keep Dadab alive after the latter's methane tank depleted. Huragok use thousands of microscopic organisms to digest the food they consume, producing many gases, including methane, as a by-product.

Geas was a Forerunner term[note 2] that referred to a genetic command imposed on an organism or species. Under the influence of a geas, an organism could be given a set of subconscious orders that would either be specific to that organism, or passed on to their children, in some cases lasting several generations. Only highly skilled Forerunner Lifeworkers, such as the Librarian, were capable of creating a geas. Forerunner students of the Mantle also hypothesized that the Precursors may have imposed a geas on the Forerunners themselves. During her stewardship of Earth and humanity, the Librarian imposed a geas upon various humans at birth; they later recalled the experience as her physically visiting them, but in reality she used an automated imprinting system of "beacons" to broadcast the geas remotely.[3] Humans who were part of the Librarian's "special population" on Earth were used as living archives,[4] with their geas containing extracted memories and personalities of their ancestors who had fought in the Human-Forerunner War. These memories required specific triggers in order to awaken within the carrier individual; for example, the ancestral memories of Chakas and Riser surfaced after they traveled to Charum Hakkor, once the heart of the human empire.[5][6] Once active, an archived personality could effectively exist as a fully aware consciousness alongside the carrier's own mind, or in some cases, even subvert their consciousness and take control of their physical body.[7] The memories of the archived individual often manifested themselves in the carrier's dreams,[8] and encompassed specific knowledge the archived individual may have had on subjects such as physics, engineering and mathematics. Gei imposed on various humans played a crucial part in the Librarian's elaborate plan to reunite with her husband, the Didact. Riser's ancestors were imprinted with a drive to pass the defenses surrounding the Didact's Cryptum in the Djamonkin Crater and create a safe path through the various traps that surrounded it. Riser himself was instructed by his geas to seek out young chamanush and find them work; this resulted in him meeting and befriending a chamanune known as Chakas.[10] Both also began to have dreams of a young Forerunner visiting them in search of treasure,[11] which soon became a reality as a Manipular called Bornstellar Makes Eternal Lasting, who had been manipulated by an ancilla secretly assigned to him by the Librarian, came to enlist the humans' guidance in finding Precursor relics. Chakas and Riser led the Manipular to the Djamonkin Crater, where the sight of the Didact's Cryptum triggered pre-programmed songs which served as verbal codes to activate the Cryptum. On Installation 07, the transplanted human populations were given a geas through a similar imprinting system. For example, in the event of encountering a strange visitor, humans were programmed to bring such curiosities to Lifeworker outposts for evaluation.[13] New or altered orders could also be triggered remotely via the beacons that transmitted the signal across the installation. Such an event occurred after Master Builder Faber seized full control of operations on the Halo; all humans born on the installation were given instructions to seek out research stations, known to the humans themselves as "Palaces of Pain".[14] Such a need to travel would manifest itself in many ways, including a seemingly innate knowledge of where to go in the event of trouble,[15] pleasing mental images of the destination, such as safety, home, food, water, or shelter, as well as a voice in one's head telling them where to go.[16] Ignoring the influence of a geas took remarkable willpower, to the point that resisting it was nearly impossible even with the conscious knowledge that it may be harmful, as demonstrated by Vinnevra's struggle to avoid her geas-induced urge to travel to a "Palace of Pain". The Librarian also imposed a broader geas on the entire human race, which has affected them a great deal throughout their history following the activation of the Halo Array. The geas includes, among other things, a familiarity with Forerunner technology and control interfaces,[18][19] as well as subconscious instructions on how to gradually achieve more sophisticated technology, including smart AIs and MJOLNIR armor.[20] In addition, as a result of the Librarian's influence on humans, the basic image of what humans view as an ideal female is based upon the Librarian.[21] Some of the features of the geas are carefully hidden and will only be activated by the right triggers, such as a latent immunity to the effects of the Composer. On Requiem, a personality imprint of the Librarian activated John-117's Composer immunity in order to allow him to defeat the Didact, who planned to use the Composer to imprison all of humanity into digital form. It was indicated she did more than this, saying she was going to advance his evolution by activating his geas, telling him she'd left humanity many gifts, of which the Composer immunity was only one.

Weaponry

Forerunner constructs and sentries use a broad variety of weapons, typically high-powered energy beams. These weapons proved to be very effective when battling the Flood, burning Flood forms to the point that they cannot be revived by their compatriots. The Forerunners have also proven to be able to merge beams together into one stream to amplify its power. The Forerunners installed and constructed these intricate beam weapons inside their paradigm Arrays, allowing them to build an army of machines to battle the Flood without sending any Forerunner to the front lines. Forerunners evidently made active use of plasma weaponry as well; the Covenant's own weapons and technology are solely based on Forerunner artifacts. It could also be that these are forerunner light-based energy weapons, yet the Covenant have not yet been able to unlock their full power, much like the Dreadnought - and are only able to produce plasma due to lower energy output. The Sentinels wield orange-colored directed energy beams, used primarily for fighting the Flood. Sentinel Majors however, have a more powerful and accurate version of the beam, which sports superior energy output, at the cost of overheating issues. These more advanced energy beams are colored blue. All variants of these Sentinel Beams can be wielded by Humans and certain Covenant races. Meanwhile, Enforcers are equipped with multiple packs of small grenades, or mortar-like explosives launched over the top of their shield. The Enforcer also boasts a pair of Pulse Beams, which fire clusters of smaller red Needler-like projectiles or bolts of energy at an incredibly high rate of fire. These pulse beams are primarily used against infantry at close range. These mammoth constructs also seem capable of lifting even tanks, using some sort of magnetic or anti-gravity grapple, before crushing the target between their massive 'arms'. The Constructors' repair beam can also be considered a weapon, but with minimal damage output. The Sentinels of Onyx had significantly more powerful weaponry. They were described to be a sphere surrounded by three floating "booms", or small pieces of armor that possessed powerful energy shields which would suddenly "pop" into place in order to deflect objects moving at high velocities.[14] Their shields are not activated by slow-moving objects, however - Team Saber used this to their advantage to destroy one of the Sentinels with rocks. Their energy weapons are described as a single, slow-charging, golden beam that could melt straight through the SPI armor of the Spartan-IIIs. SPARTAN-058 had also noted that one blast from these weapons was enough to drain the shields of her MJOLNIR Mk V armor. The Onyx Sentinels also have the ability to combine for different purposes, such as exponentially increasing their combat capabilities, or for large-scale excavation. One formation of these combined Sentinels was able to easily destroy two Covenant destroyers. However, it should be noted that the second Covenant Destroyer was caught off guard after a Slipspace jump, and the first one had its energy shields down in a gesture of peace, trying to initiate contact with the forerunner constructs. The Forerunners also constructed Automated Turrets that fire blue beams similar to those of sentinel majors. These turrets themselves resemble stripped-down sentinels, and hover in mid-air, tracking enemy targets, but are otherwise immobile. In Halo 3, it seemed that even the Monitors had the ability to defend themselves against the Flood using a focused beam similar to the Sentinel's beam, but much more powerful. 343 Guilty Spark displayed this ability in Floodgate, The Covenant and Halo. The weapon was capable of draining the shields of a Spartan-II in one blast and mortally wounding Sergeant Major Avery Johnson. It is also quite odd and puzzling as to why 2401 Penitent Tangent didn't use this ability against the Gravemind in Halo 2. It is assumed that the Gravemind is likely to have damaged 2401 Penitent Tangent when he captured the Monitor, disabling its beam weaponry. It could simply be that it was not equipped with one, although this is highly unlikely due to the importance of the monitors to ensure the Halo Station's upkeep.

War Sphinxes were midsize Forerunner fighting suits, twelve of which were left on Earth during the Human-Forerunner War. By the time Bornstellar Makes Eternal Lasting visited the planet, the suits were considered antiquated and outdated.[1] The suits were described as being ten meters high and twenty long, with an elongated tail that provided lift and power. From the "tail" rose a large rounded torso with a command cabin perched on top. War Sphinxes are programmed to contain samples of their wearer's mental patterns and personalities before they are killed in battle. These preserved personalities are less realistic or complete than Durances, but can still be studied by a commander to gain useful information. The Didact kept the final impressions of his children, who were killed in battle, within their War Sphinxes.

The Despair-class hunter-killer was a classification of Forerunner war machine. They were described as curved and sleek in design. Despair-class hunter-killers were present at the Battle of Janjur Qom.

The Diversion-class was a classification of Forerunner military construct. Several Diversion-class war machines were present at Janjur Qom during a San 'Shyuum uprising.

Seekers were mechanized armor-suits used by Forerunner Warrior-Servants. They are newer and more advanced versions of the outdated war sphinx. Seekers were longer and more streamlined than war sphinxes, and were equipped with more powerful movement and defensive capabilities. They lacked the "face" that adorned the command cabin of a war sphinx.

The Automated Turret, also known as the Auto-Turret, is a form of equipment similar in design to a Sentinel. As its name implies, it acts as an automatic defense system (deployable antipersonnel turret) for the player and is featured in Halo 3. It is so far only encountered on the Halo 3 levels The Ark, The Covenant and Halo, and is not found on any multiplayer maps due to the issue of keeping the game balanced, and it's inability to work with multiplayer netcode. The auto-turret is best dropped in an area where you want to defend; once deployed, it will automatically shoot at the enemy if they are within the turret's sight

The Pulse Beam fires a rapid stream of small, red semisolid energy bolts. These projectiles are very similar in appearance to that of the Needler, but do not have the homing or explosive abilities that the Needler has. Once the projectiles have made punctured an enemy, they "shatter" within a few seconds, just like Needler rounds. However, pulse beams do not create the same explosion as Needler rounds do when stuck with 7 or more projectiles. They travel a considerable range and gradually lose altitude as they fly, giving Enforcers a decent advantage over the Flood as they can fire from long ranges and heights. The Pulse Beam is designed to effectively combat the Flood by vaporizing the host bodies and Flood forms to prevent reanimation. Due to the sheer amount of projectiles fired at once, and due to the sharpness of the projectiles, the projectiles easily penetrate flesh and most armor. Presumably, the explosion caused by the projectiles also aids in shredding Flood biomatter. Since the projectiles have high energy power, they are also useful for combating other sentient beings, such as Spartans and Elites. However, like other attached weapons, they can be blown off to render the Enforcer harmless. The pulse beam is only one weapon used by the Enforcers, and is generally intended for use against infantry. The weapon is mostly ineffective against vehicles, so a more suitable weapon is used in its place. While the weapon can be deadly, it is generally weak if appropriately avoided. Individual projectiles are of little consequence, but the player should avoid being hit by multiple projectiles, as they easily bring down shields.

The Forerunner Missile Launcher is a missile weapon found exclusively on the backs of Enforcers. Fired in an upward arc, not unlike the Wraith's plasma mortar, it is highly destructive, and has seemingly unlimited ammunition. The player cannot wield the missile. It is unusual that the Forerunners created such a weapon, as they tended to favor beam weapons over all other weapons. They are seen only in Halo 2, as their wielders, Enforcers, are only seen here.

The Sentinel Beam is a Forerunner directed energy weapon used by Sentinels. The weapon is particularly effective against small Flood outbreaks, and is efficient at stripping energy shields. Although typically integrated into the structure of a Sentinel, it can be used as a hand-held weapon if scavenged from a destroyed Sentinel. The blue Sentinel Beam used by the Sentinel Majors is a more powerful variant of the common yellow-orange Sentinel Beam, though it also overheats more quickly and its charge depletes faster. This difference is very similar to the relationship between the Plasma Rifle and the Brute Plasma Rifle. The beams used by the Sentinels at Onyx were a golden color, with temperatures as high as 15,000 Kelvin.[1] Although this variation of the weapon took significantly longer to charge, it is thought to have been capable of depleting a fully shielded MJOLNIR Armor suit. Furthermore, Onyx Sentinels were capable of cooperating to generate golden beams capable of destroying entire Covenant Cruisers. The power of the beams is one of many differences documented in the Sentinel variant's article; such differences are likely because Onyx Sentinels were guarding something even more important than the Halo Array: the Shield Worlds.

The Archon was a handheld energy weapon created and used by the Forerunners during the Forerunner-Flood War.[1] It was a white, claw shaped device that fired a bright blue bolt of energy. Upon activation the weapon generated what appeared to be a blade of some sort, capable, as previously stated, of firing bolts of energy. When multiple weapons were used in conjunction, they could apparently combine their energy bolts to form a single large blade-like projectile that sliced through the air.

Destructor beams were Forerunner directed energy weapons mounted on Forerunner capital ships.[1] Four cruisers firing destructor beams at the same time were able to shred a Halo installation.

Forerunner Particle Cannons are weapons used by the Forerunners during the Human-Promethean War. Forerunner Particle Cannons are enormous floating platforms used by the Forerunners as anti-air defences. Particle Cannons project a beam of energy similar to a Sentinel Beam to disintegrate any target in range. They are however vulnerable to ground based attacks and are structurally weak in the centre, as when a shot is fired into their primary weapon, the entire cannon is destroyed. A number of these weapons were encountered on Requiem in use by the Prometheans as anti-air defences, destroying a number of Pelicans and killing a number of Marines in the process. These cannons were destroyed by the Mammoth deployed to the surface by the UNSC Infinity, with the Master Chief providing targeting for the Mammoth. These cannons were controlled from a central core via an AI, before it was deactivated by Cortana.

Forerunner Beam Turrets are weapons used by the Prometheans during the Human-Promethean War. Forerunner Beam Turrets are turrets of a similar nature to those located on Shield 049, but smaller in scale. They are typically constructed by Watchers and possess a deadly, long range beam weapon, akin to a Sentinel Beam. When destroyed, Forerunner Beam Turrets disintegrate in a manner resembling that of Promethean Knights. A number of these turrets are hacked by Cortana on the Mantle's Approach during the Battle of Earth during which time they took on a blue light, like those of the Sentinels on Requiem.

Pain Projectors were Forerunner devices used to administer pain to a subject for punishment or torture purposes.

The Composer was an ancient Forerunner machine capable of converting living beings into digital forms. The Composer was created by the Forerunners to save them from the Flood by allowing them to transcend biological forms altogether, granting them virtual immortality as digital intelligences. However, the Forerunners never perfectly mastered this capability and the resulting digital personalities became corrupted or fragmented and could no longer be restored to biological form. The Composer was also capable of slowing down Flood infection and the subsequent loss of individuality; however, this process was only temporary and still left the afflicted individuals in their deformed state. Physically, the Composer was an enormous, monolithic artifact engraved with patterns of lines characteristic of Forerunner architecture. The first known use of the Composer was when the Librarian employed its primary capability by extracting the memories of the surviving human warriors after the Charum Hakkor campaign in order to store their memory impressions in future generations of humans. The Lord of Admirals, supreme commander of all human forces and one of the humans to have their minds harvested, never saw the Composer directly and described its presence as "strange, ever-changing" and "multiformed", as it operated via intermediary Lifeworker machinery. As a result of the risks and irregularities involved with its usage, the Forerunners eventually abandoned the Composer and its existence was made a closely guarded secret known only to few. Even its actual nature remained obscure; whether it was a machine or being remained uncertain to most. Some even believed the Composer to be a "product of its own services"; a Forerunner, perhaps a Lifeworker, suspended in the final stages of Flood infection. Around 100,000 BCE, the Composer was used by the Master Builder to stave off Flood infection in certain Forerunners on Installation 07 to keep them in a docile state. After initial processing with the Composer, a form of harness prevented the infectees' decaying bodies from breaking down. While in control of Installation 07, Mendicant Bias and the Primordial also used the Composer to extract the ancestral memory imprints from Chakas and the other humans from Earth. Later during the Forerunner-Flood war, the Didact used the Composer to convert his Promethean warriors into robotic forms in order to allow them to combat the Flood more efficiently and without risk of infection. To bolster his numbers, the Didact used the Composer on a human population on Installation 07, turning them into additional forces in his mechanized army. The Composer later ended up in an asteroid field orbiting Installation 03. After the end of the Human-Covenant War, the United Nations Space Command Office of Naval Intelligence discovered the machine embedded in an asteroid and set up a research facility known as Ivanoff to study the artifact. Upon awakening on Requiem in 2557, the Didact immediately headed for the Composer and acquired it. Planning to use the device to neutralize all of mankind by forever imprisoning them into digital form, he first used it on the human personnel of Ivanoff; John-117 was the only survivor as a result of genetic modifications imbued by the Librarian. The Didact then set course for Earth in order to realize the final stage of his plan. The Didact successfully fired the Composer on an URNA metropolis, New Phoenix, but the effect was halted when John-117 destroyed the Didact's ship, and the Composer along with it, with a HAVOK tactical nuclear weapon.

Art and architecture

Forerunner architecture is noted mainly for being large-scale and geometric in style, with a semi-triangular theme being the most commonly observed design. The Forerunners were highly skilled at creating natural-looking habitats, such as those of the Halo rings, which tend to be very elaborate, with numerous extrapolations of the basic design of a construct appearing to be purely decorative. In addition, the structures were engineered to compliment the natural landscape, as opposed to the modern idea of replacing it. That said, their distinctive beauty are not restricted to Halo Array network. The Aztec-esque stones of Cote D'Azur, the arches and weathered inscriptions of Sigma Octanus IV, the intricate caverns and three-kilometer holographic dome beneath ONI's Reach complex, the ancient stepping-stones of the Grunt's homeworld, and the Forerunner City discovered in the depths of the human-inhabited Onyx, all display the Forerunner's innovative architectures. Most Forerunner architecture is constructed with a special type of metal that resists deterioration, bullets, plasma bolts and fire, as made evident by Forerunner structures standing in pristine condition 100,000-150,500 years after they were built. However their resistance to plasma fire is limited; in Halo: Ghosts of Onyx the Elites blasted a hole in a Forerunner wall with plasma weapons. In Halo 2, Sgt. Avery Johnson destroyed the door to the control room of Delta Halo with a Scarab. Other structures are constructed out of traditional materials, such as chalcedonic quartz, which does not preserve nearly so well. These structures employ complex geometric shapes that appear to operate in dimensions higher than human understanding can comprehend.[14] The Forerunners also decorated the interiors of their structures with a complex web of engraved straight lines and applied decorative touches and designs to nearly everything that they built, from structures to weapons. Even the Sentinel robotic drones possess small holographic Forerunner script around their "eyes". Forerunner architecture distinguishes itself from Covenant structures in that they incorporate heavy use of geometric angles, usually at either extremely sharp degrees (as the Forerunner buildings are usually triangular), or at forty-five degree angles, most notably seen in Halo: Combat Evolved . Originally, the ideas and concepts on Forerunner structures and technology was that it would be sleek and curved to give it an advanced feel. However, Bungie wanted the structures to feel as if they could stand the test of time and redesigned them to be solid and monolithic. The smooth, near-organic design would later be adopted by the Covenant in their architecture, although they did not adopt the Forerunner tradition of decorating their structures with glyphs. In Halo Wars the Forerunner counting system is used to open and close portals on the last level.

Sentinel Walls are massive walls built by a Halo Installation's Sentinels in the event of a severe Flood outbreak. A Sentinel Wall surrounded the Quarantine Zone around the Library of Installation 05 to keep the Flood from spreading. The Wall appears to have been designed to keep the outbreak of Flood around Delta Halo's Library contained within the Quarantine Zone. It is honeycombed with tunnels for the Sentinels to travel through. Sentinels and Enforcers keep the Flood contained, while Constructors keep repairing the damage that the Flood inflict on the wall. It is possible that there is a constant battle in the Quarantine Zone, as in the level of the same name, Flood and Sentinels are seen in many instances fighting one another. In addition to the massive physical wall, the Sentinel Wall also projected an energy barrier known as a Containment Shield.

The Sentinel Factory is a unique Forerunner unit building structure in Halo Wars. The structure is a type of Sentinel Constructor Factory, and it is able to construct additional combat support in the form of Sentinels once captured by a player, which can then be added to their forces. The structure can also be captured again by an enemy player, so must be defended. While this building does not need to be garrisoned, player's units must be near it. There's usually a good amount of fighting over these online, so if you're holding it, it's best to have it guarded by a few infantry squads. The Sentinel Factory is only found on the multiplayer maps Repository and Glacial Ravine. The Sentinel Factory produces Sentinels for 100 resources, and Super Sentinels for 250 resources. The sentinels are produced instantly and they must recharge before being able to produce a new unit, much like the Support Abilities of the UNSC.

Forerunner Forts in Halo Wars are outposts guarded by large beam turrets and Sentinels. It also is surrounded by shield walls with ends meeting at the turrets. They are capable of retracting in on itself after sustaining enough damage. Twenty seconds after the fort retracts, it is available as a base location.

Sentinel Constructor Factories are facilities that manufacture various types of Forerunner automatons, such as Sentinels, Sentinel Majors and Enforcers, or in case of Onyx, Onyx Sentinels. The appearances and sizes of these facilities vary greatly depending on their location. There are several varieties of Sentinel factory. The most commonly seen are massive, floating structures that hover above battlefields. These facilities were used during the Flood outbreak on Installation 05, and could be seen in the sky above the Quarantine Zone around the Installation's Library. Onyx contained a massive Sentinel factory located underneath its north pole, which produced the huge number of specialized Onyx Sentinels that made up the artificial planet's superstructure. The Sentinels in this facility were constructed out of molten ore spewed from a massive machine, which cascaded into a hollow tower. From the bottom of this tower tumbled millions of Sentinel components, which then were ferried to another part of the factory by energy beams. As they traveled, they assembled themselves into the three-meter long "booms" of the Onyx Sentinels. In the center room, there was a pyramid-shaped structure described as being "five times the height of the Great Pyramid of Giza", which was composed of the "eye" spheres of the Sentinels. Every six seconds a sphere from the apex of the pyramid ascended in a shaft of silver light. When the spheres emerged, they had been assembled into a complete Onyx Sentinel.[1] Another Shield World - type installation discovered by the crew of the UNSC Spirit of Fire had several types of underground Sentinel factories, which created standard Sentinels, Super Sentinels and Protectors.

Forerunner astroengineering

While the Forerunners' architectural and technological prowess is legendary among the Covenant and UNSC, their masterpieces also extended to the fields of stellar engineering. At least three Forerunner sites, the Shield World[14] Onyx, the Ark[17], and the Micro Dyson Sphere that holds the Apex, made use of suns where none should exist. The Shield World existed permanently in Slipspace, where solar systems outside of a Dyson Sphere cannot exist, and the Ark was located far outside of the galaxy where galactic material would have been insufficient to form the sun that illuminates the Ark. The sun at the center of the Dyson Sphere where the Apex was housed was abnormally small, in order to accommodate the planet-sized Dyson Sphere. Whether these suns are artificially engineered or simply moved from another star system by the Forerunner is unknown: either would have been an enormous technological achievement. Another known Shield World is the planet discovered by the Spirit of Fire. This world had an outer crust like Onyx, but its inner Dyson sphere was accessed through a long narrow tunnel hidden under one of the planets oceans. Once through the tunnel, the Spirit of Fire had to pass through several "cleansing rings" in order to make it to the center of the planet. This Dyson sphere, unlike the Onyx Dyson sphere, was not separated in slipspace but was actually constructed on what appeared to be hollowed out inside of the planet. This sphere seemed to have had an artificially created sun like the one on the Ark. The Ark is confirmed to be artificial, due to its unnatural "flower head" shape. It is likewise unknown if these are the only stellar engineering achievements the Forerunners made. However, it is clear that manipulation of slipstream space allowed the Forerunners to transport and position these structures throughout the galaxy.

The Capital was the political center of the Forerunner ecumene. It was a massive structure, greatly exceeding the scale of even the Halo installations. The capital was one of the oldest structures in the ecumene, having been constructed roughly around 125,000 BCE.[2] It housed a population of several hundred thousand Forerunners, mostly high-ranking Builders. Trillions of ancillas served in the capital in the capital metarchy, an enormous network coordinated by a Metarch-level ancilla that answered to the chief councilor. It was one of the most trafficked locations in the ecumene, with constant security patrols, sentinels, and transports swarming around it.[1] Within five thousand kilometers of the structure, incoming vessels would be carefully screened by sensory fields and directed by hard light docking nets.[3] The capital's system housed multiple slipspace portals that linked to many worlds, as well as the Ark. The capital was composed of a series of perfectly circular "platforms" arranged in a spiral along a central rod. These platforms decreased in size toward either end of the rod, with the widest central one being approximately 100,000 kilometers in diameter. Each platform was covered with a "city" of structures and buildings,[1] whose gravity was controlled individually by buffer fields. The capital was home to the Council amphitheater, where the Ecumene Council engaged in debate on important matters. The amphitheater was suspended in midair, attached to the rest of the capital by bridges, anti-gravity gondolas, and lift tubes for individual Councilors. During Council proceedings, the amphitheater would be decorated with display spheres showing representations of the twelve of the systems inhabited by early Forerunners, each carrying an epistle of the Mantle. Near the Council amphitheater there was a hallway with its walls decorated with countless spent slipspace flakes, some of which had also been built into sculptures. In the event of a large-scale attack, the capital could rotate its sections to assume a spherical shape, thus protecting the structures atop each platform from damage. It also possessed powerful energy shields and a large defensive fleet. If the capital metarchy coordinating the fleet was compromised, the fleet would splinter into individual squadrons, each having specific instructions on how to deal with an attack.

The Halo Array is a network of seven ring-shaped artificial worlds created by the Forerunners in order to kill all sentient life within range of the array, virtually the entire galaxy.[5] Rather than a weapon of war, these were used as a last resort against the Flood, a parasitic extra-galactic species that threatened to infest every sentient lifeform in the galaxy. By activating the rings, the Forerunners denied the Flood access to these lifeforms, effectively starving the species to virtual extinction, though it clung to life in a number of Forerunner facilities, including some Halo installations.[6] The two known Halo installations, referred to as Alpha Halo and Delta Halo respectively, orbit gas giants, though it is not known whether this is the case of all the Halos, and Alpha Halo maintained an atmospheric mining facility until it was destroyed by the Covenant.[7] Though separated by thousands of light-years, the seven installations are networked together and capable of remote activation at the Ark, an installation outside the galaxy. Each Halo installation has a maximum effective range of 25,000 light-years.[8] The exact means the array uses to conduct this "mass sterilization protocol"[9] are unknown, though it is assumed to utilize energy in some type of form. The Halo Array in its entirety has been fired once in known history, approximately 100,000 years ago, by the Didact[10] in order to stop the Flood from overwhelming the galaxy. Despite being the network's builders, the Forerunners were killed in this last suicidal attempt to save the rest of the universe from a worse fate.[5] The array has nearly been activated three times since; Alpha Halo was almost activated by the Master Chief before being deactivated by Cortana, while Delta Halo was activated by Commander Miranda Keyes, forced by the Chieftain of the Jiralhanae Tartarus, and Sergeant Johnson was forced by the Prophet of Truth to activate the Ark. None of these attempts were successful. A replacement Halo for the destroyed Alpha Halo was activated outside of the array's range, eliminating the freed Flood, but did not activate the rest of the array.[11] Each Halo Installation is given a designation number, from 01 to 07, and is overseen by a Monitor. The Monitors are given control of the Installations' Sentinels, Constructors and Enforcers, and are responsible for containing the Flood test subjects in their research facilities and protecting the Halo from intruders. The Array also encompasses an installation known as the Ark or Installation 00, from which the array can be remotely and safely activated while out of firing range. Inhabitants on the Ark are able to survive the effects.[12] The Forerunners also built active Shield Worlds, Micro Dyson Spheres encased in a slipspace field with their own star in the center and a habitable environment, as a means to escape the effect without having to leave the galaxy.[13]

Installation 00 resembles a massive flattened dish with a series of eight curved arms, similar to the petals of a flower and bearing similarities to a sun . The Ark Core is the stripped remnant of a material-rich planetoid, asteroid, or other celestial body used for the construction of the Halos, which the Ark constructs. The entire upper surface is terraformed, with oceans, forests and even a large desert, where John-117 first makes landfall. At the time of construction, the Ark lacked its core and a livable surface with no land or water. The structure is the second largest known Forerunner construct, only dwarfed by the the Micro Dyson Sphere, which has a diameter of 300 million kilometers. A simple inspection of the holographic representation reveals the Ark to be anywhere from 90,000 to 100,000 kilometers (55,890 to 62,100 miles) in diameter.[5] The three shown primary functions of Installation 00 are as a remote for activating the entire Halo network while safely out of the Halos' range, as an automated construction facility for the creation of replacement Halo installations (ensuring that the network continues to operate even if any rings are destroyed), and it has also been confirmed that the Ark was meant to be used to reseed the galaxy in the event of the Halo arrays being fired. Held deep within its mysteries was a collection of every species the Forerunners had studied and governed over. How this plan was to be initiated is still unknown. Most interestingly, the Ark is not actually in the Milky Way as noted by a stunned ODST soldier at the start of the level The Ark. The Ark is in the void in between galaxies, known as intergalactic space. As such, it's outside the believed range of any Halo installation. The Ark also has an artificial sun floating above it. An observer can see this more clearly on the level Halo when looking up at the sky.

Planetary Shields were a variant of Forerunner energy shielding technology that could be extended to cover entire planets to protect from stellar radiation. Sections of a planetary shield could be temporarily lowered to allow starships to pass through. Normally, a planetary shield was barely visible, but caused noticeable refraction when opening or during sunset. The homeworld of Bornstellar Makes Eternal Lasting was protected by a planetary shield.

The Quarantine Shield was a Dyson sphere, more specifically a variation of the concept known as a Dyson swarm, composed of trillions of vigilants, formed by the Forerunners around the San 'Shyuum quarantine system which included the planet Janjur Qom. The shield extended four hundred million kilometers from the system's star, and required special access codes to pass through.[1] If the population inside the sphere showed signs of unrest, the shield would enter "battle mode", heightening the vigilants' combat readiness.

The Greater Ark, also referred to as the Ark or the Beginning Place,[1][note 2] was a Forerunner megastructure, and one of the two Arks used to manufacture Halo rings. It was known to have produced the original Halo Array, comprised of rings 30,000 kilometers in diameter as opposed to the 10,000 kilometers of the final Array, which was produced by the smaller Installation 00 instead.[2] Like Installation 00, the greater Ark was located outside the Milky Way galaxy. Though it shared Installation 00's flower-like shape, consisting of a series of curved arms extending from a circular central section,[3] the greater Ark differed from the lesser Ark in a number of respects;[note 2] it only possessed six petals, as opposed to the eight arms of Installation 00.[4] Instead of an artificial sun, the greater Ark was illuminated by six shafts of plasma, each suspended over one of the petals, emanating from a tower structure in the center.[5] These plasma tubes would dim and brighten cyclically, approximating a day-night cycle.[6] Each of the greater Ark's arms possessed at least one petal station, from which Forerunner Lifeworkers operated

A Shield World is a Forerunner installation, designed to be a shelter from the activation of the Halo Array. The main component of a Shield World is a complete and thorough Micro Dyson Sphere, located within a Slipspace bubble of compressed space-time. The only way in is a small portal that constitutes the only real-space component of a Shield World. Access to Shield Worlds was only possible upon the imminent activation of the Halo Array.[1] The Dyson Sphere within a Shield World is two astronomical units, ie. 300 million kilometers in diameter, and its inner surface is entirely terraformed and capable of supporting life. In the center is an artificial star. The inner Dyson Sphere resides within a Slipspace transit, accessible only from the Core Room Antechamber in the heart of the artificial planet formed around the structure. In normal space, the slipspace bubble is radically smaller than the interior, being only a few meters in diameter. Over a thousand years prior to the second coming of the Flood, The Shield Worlds were proposed by the Didact as refuges from the Halo Array's pulse. However, the betrayal by the Forerunner AI Mendicant Bias and its defection to the Flood forced the Forerunners to abandon their plans to evacuate into the shield installations, as Mendicant Bias revealed the locations of the Shield Worlds to the Flood.

Forerunner AI

A metarchy was a vast network of Forerunner artificial intelligences composed mostly of ancillas and monitors, and was coordinated by a metarch-level ancilla. Most of the ancillas in a metarchy were disembodied and never assumed visible form.[1] There were several significant metarchies, including the Council metarchy located at the capital and the metarchy used by the Librarian.[2] The Council metarchy answered to the Forerunner chief councilor,[3] and coordinated all operations within the capital, including its defense.

Metarchs were a class of hyper-advanced ancillas created by the Forerunners to serve the Council. They were so exclusive that only five were in existence at any given time.[1] Enormous ancilla networks known as metarchies were coordinated by a metarch. Mendicant Bias was considered a Metarch-class ancilla, though he was technically a Contender-class AI and therefore more advanced than even a Metarch.

Ancillas are a type of Forerunner artificial intelligence. They come in several varieties, each designed for different purposes and possessing differing capabilities. They can be stored within a Forerunner's armor, able to be accessed by a user at will. Ancillas can also be housed within personal shells like those of the Monitors, ships, buildings and various forms of machinery. They typically possess personalities approximating that of a Forerunner, and in this respect are quite similar to UNSC "Smart" AIs.

The Contender-class artificial intelligence was a class of Forerunner artificial intelligence, or Ancilla, that was the most advanced of its time.[1] A Contender-class AI was composed of numerous AI "minds" or instances working in sychrony, thus giving it intellectual capabilities far beyond any other AI. This class of AI could command an entire fleet of ships, with its consciousness being housed in several "core ships". During the Forerunner-Flood War, the Forerunners created Mendicant Bias, the first Contender-class AI. Mendicant Bias was designed with the sole purpose of engaging in discourse with the parasite’s central intellect, the Gravemind, and then gathering information from it. When instructed by the Forerunners, the AI would use the information gathered about the parasite's weaknesses to unrelentingly attack the Mind until the Flood withdrew from the galaxy or perished

A daemon is a computer program that performs its function "in the background" during the normal operation of a computer system, for example providing security services, performing maintenance operations, communication with peripherals or other subsystems, or more. The Terminals located on Installation 00 stated that daemons tried to prevent Mendicant Bias from communicating with the Reclaimer. He may have used the phrase to refer to other Forerunner artificial intelligences on Installation 00 [1], or more likely uncontrollable background processes.

The Monitors are highly advanced Artificial Intelligence constructs created by the Forerunners at least 100,000 years ago to occupy special positions in Forerunner society. One of their main purposes was to service and maintain the Halo installations and to ensure that the virulent Flood stayed imprisoned. Other purposes include the maintenance of Line Installations. Monitors are extremely intelligent, yet completely devoted to their original function, and are zealous about containing Flood; Monitors have been known to turn violently on their allies if they should attempt to violate their containment protocols. Each Halo Installation has at least one Monitor assigned to it, with Installation 05 having two: 2401 Penitent Tangent, and a large Monitor on a monorail, seen in Halo 3's Cold Storage. Monitors have both numbers (presumably for identification) and names. A Monitor's identification number appears to be 7 raised to the power of the Monitor's Installation number minus one. The names appear to consist of an adjective describing a negative emotion followed by a technological term, though neither of the two names seen appear to have any specific meaning. In Forerunner communication logs, Monitors are identified by their Installation number (padded to two digits), a dash, and their own number; for example, 343 Guilty Spark, Monitor of Installation 04, is identified on such logs as "04-343." Each Monitor commands the Constructors, Sentinels, Sentinel Majors, and Enforcers of the Installation they monitor.[2] The latter two are only activated if a catastrophic outbreak occurs, to hold back the Flood, while the Monitor locates a Reclaimer. Monitors are extremely intelligent, but are also devoted to their original functions and to protocol, resulting in (among other things) a zealous attitude toward containment of the Flood and an overeagerness to activate the Halos. Monitors frequently cite protocols as explanations for their actions, no matter how impractical; this has been known to confuse or annoy humans who have interacted with them. It is possible that a Monitor sees their protocols as the only options in a situation; in Halo: Combat Evolved, 343 Guilty Spark could have taken numerous precautions to prevent the Flood from spreading across the Installation, but the only action he ever considered was the activation of the Halo. Nearly every action taken by a Monitor is based on some sort of protocol; even their greetings appear to be standardized. Of the two Monitors seen in the Halo series, both have introduced themselves as follows: "Greetings. I am [Number] [Name]. I am the Monitor of Installation [Number]."[3][4] The only variation seen is the occasional reversal of the latter two sentences. Though a Monitor's knowledge of its own Installation is seemingly limitless, Monitors' knowledge is otherwise quite limited. In particular, 343 Guilty Spark does not appear to be able to distinguish between different Reclaimers until the events of Halo 2 [5],[note 2] and the construct has admitted to a lack of knowledge about other Installations, and it can be assumed that the Forerunners practiced this compartmentalization of information with the other Monitors as well.[1] Monitors keep daily logs of all things that occur on their Installation. As with UNSC AI, the Monitors have been speculated to be in stages of Rampancy -- a condition that affects human "Smart" AIs and is comparable to insanity—due to their isolation for literally a hundred thousand years. Monitors seem to have a defensive resistance to small arms fire, though they will eventually succumb after taking extensive damage. In the novel, Halo: The Flood, Master Chief fired half a magazine from an MA5B Assault Rifle at 343 Guilty Spark with no apparent effect; on Installation 04 (II), the Master Chief was only able to destroy the Monitor with four blasts from a Spartan Laser, demonstrating that Monitors can sustain damage from high power weaponry. By comparison, a Spartan Laser can destroy virtually any other object in two shots or less. Should a Monitor be damaged, it is capable of self-repair.[6] Though Monitors are assisted by other constructs in the event of a Flood outbreak, the Monitors also have their own offensive capabilities, including three types of beams. The first beam allows a Monitor to manipulate and levitate objects[7]; the second beam is a red-colored beam capable of depleting the shields of a Spartan-II in MJOLNIR Mark VI armor in a single blast and mortally wounding a less-armored human[8]; and the third is a blue beam that is primarily meant for unlocking doors on Forerunner structures, but that can also inflict minor damage upon targets.[1] Monitors have the ability to teleport themselves and others around their Installations. It is unclear exactly how this teleportation works, but it seems that a Monitor on an Installation other than its own has no access to that Installation's transportation grid. It is possible that these limits are programmatic rather than physical; after hacking into The Core of a Halo, the human AI Cortana gained the ability to access the teleportation grids of all Installations, though her inability to access the power grids restricted her usage of the grid.[9] In Halo: Ghosts of Onyx, Dr. Halsey comments that Onyx's teleportation matrix is powered by a Slipspace generator of some sort; the Monitors may use similar technology when teleporting.

Forerunner Military

Warrior-Servants or Warriors were the second-lowest rate in Forerunner society. As their name suggests, they were responsible for defense and warfare in the Forerunner ecumene.[1] The Warrior-Servants were presumably all subordinate to the Warrior-Servant Corps.[2] They utilized many different war machines, including war sphinxes. Warrior-Servants were powerfully built, and typically taller than the other rates such as Builders.[3] While Forerunner society was peaceful by nature, Warrior-Servants were ruthless in executing warfare against enemies of the Ecumene, as they believed that defying the Forerunners was to show contempt toward the Mantle itself.[4] Although their services were vital in maintaining galactic harmony, most Forerunners viewed their purpose and practices as being contradictory to the principles of the Mantle. As such, other rates looked down on the Warrior-Servants, who mostly kept to themselves as a result.  It was a common policy among Warriors to harvest the memories of their vanquished foes before executing them. The highest class of Warrior-Servants, known as the Prometheans,[7] had once been in high social standing and power, serving in various roles in the Forerunner Council. However, after the conclusion of the Human-Forerunner wars, the Prometheans were opposed to a Builder plan to construct a new superweapon known as the Halo Array. Circa 101,000 BCE, the Prometheans lost this political battle and were removed from the Council,[8] some of them entering self-imposed exile in "Warrior Keeps" known as Cryptums, while others were executed.[9] This also resulted in the entire Warrior-Servant rate being marginalized, with their fleets and armies being systematically disbanded over the course of the next millennium.[8] This would leave the ecumene ill-prepared for the return of the Flood.

The Prometheans were the highest and most respected group of Warrior-Servants in the Forerunner ecumene. During and after the Human-Forerunner War, they were led by the Didact. During the Forerunner-Flood war, the Prometheans' main base of operations was the fortress world known as Requiem. Elements of the Prometheans survived the Forerunner-Flood war and the activation of the Halo Array, eventually awakening within Requiem and rising to oppose the UNSC in 2557. Physically, Prometheans were the highest form a Warrior-Servant could mutate to, standing around two times the height of a Forerunner Manipular and weighing about four or five times a Manipular's mass. They were heavily muscled, their hands capable of easily crushing a human. Their mental capabilities were also very sophisticated; it was common for a Promethean to share information and sensory input with the warriors under their command. Prometheans were also capable of controlling a million remote-controlled craft, such as weapon-ships, simultaneously. They also used powerful vehicles known as war sphinxes for large-scale operations. In order to combat the parasitic Flood during the Forerunner-Flood war, the Prometheans' arsenal of weapons was specifically tailored to disintegrate biomass to prevent Flood infection. The Prometheans were responsible for creating "Warrior Keeps" known as Cryptums, where an exiled warrior could live in suspended animation for thousands of years.

The Forerunner Navy was a branch of the Forerunner Armed Forces. It was led by Forerunner Fleet Command and was in charge of all space combat and naval operations. They held the responsibility of protecting Forerunner planets from space from the Flood in the Forerunner-Flood War.[1] It is unknown exactly how many ships that the Forerunners had in their fleet, but given that a single AI would take personal command of a core fleet alone of one thousand ships, it is fair to assume that the Forerunner fleet consisted of many thousands of ships, though this number was severely whittled down over three centuries of war. During the course of the war, the Forerunner fleet attempted to prevent the Flood from landing on the surface of various planets, and when the Flood invariably did, the Forerunner Navy's main concern was to evacuate as many civilians as possible. As the Forerunners realized that they had no chance of militarily winning the war, and as the Flood closed in on the Maginot Sphere, they created a master AI, Mendicant Bias, to coordinate all of their strategic movements and grapple with the Gravemind itself. Mendicant Bias was given a personal fleet of a thousand core capital ships. However, direct contact with the Gravemind caused Mendicant Bias to turn rampant, and it quickly turned on its creators. Mendicant Bias led its fleet through the Maginot Sphere, where it encountered three entire fleets of Forerunner warships led by Offensive Bias. The following encounter was quite possibly the largest battle ever seen by the galaxy ensued between the two opposing sides. At this point, Didact, overall commander of the remaining Forerunner Navy, fired the Halo Array. Although it killed all the surviving Forerunners, it also neutralized Mendicant Bias's giant Flood-controlled fleet, which had until this point, vastly outnumbered Offensive Bias. With the odds much more even, Offensive Bias managed to defeat the rampant AI's remaining core ships and attempted to deliver Mendicant Bias to the Ark for study.[1] What happened to the few surviving Forerunner ships after this is unknown, but without any Forerunners to guide them, some of them may have crashed onto various objects and were later found by the races of the Covenant, some utilizing the ships' advanced technology. For example, the Forerunner Dreadnought was used to power the Covenant capital of High Charity.[2] Based on what was seen of them, Forerunner vessels were massive and extremely well protected and powered. A single Keyship could power a structure the size of an entire moon;[3] and this only required a fraction of its total power output.[2] In a UNSC naval assault against the Covenant Loyalists in the Battle of Voi, three UNSC Frigates fired their Magnetic Accelerator Cannons at the Forerunner Dreadnought but it remained intact.[4] This makes it even more powerful than a Covenant Supercruiser, which could only barely take the impact of three special light MAC rounds and five hundred Archer missiles. However, it has never been seen to use its actual weapons. The Unnamed Forerunner Starship can combine their fire into a large singular beam capable of slicing a ship in two, before causing a massive explosion.

Forerunner Fleet Command[1] was a Forerunner military organization in command of the Forerunner Navy and possibly the entire Forerunner military, including the Suppression Fleet, Security Fleet and Emergency Circumstance Fleet. During the final stages of the Forerunner-Flood War, Fleet Command ordered that all personnel register their equipment keycodes with them. It is likely that Didact commanded it, as he seemed to be the overall Forerunner military commander.

Spacecraft:  Forerunner spacecraft used special crystals to travel through slipspace. In order to move through ordinary space, they utilized a reaction drive which harnessed virtual particles as a propulsive force. Certain Forerunner ships could be "grown" from a design "seed", unfolding from a highly compact state into a fully functional spacecraft. At least some types of Forerunner craft can alter their geometry to better suit their current situation, for example, making the ship more areodynamic in preperation for surface landing.

Classes of Ships

Council ships were a class of vessel used by Forerunner Councilors. The hull of a Council ship has been described as "a double upsweep of winds cast in bronze and gold." They were one of the most advanced ships in the Forerunner Ecumene, superior to larger military vessels in all but weaponry.

Dignity-class escorts were escort vessels used by Builder Security. The escorts were used on Janjur Qom during the battle on the planet.[1]

Falco-class space pods were small Forerunner evacuation craft normally attached to large interstellar craft. During the Battle of the Capital, Bornstellar Makes Eternal Lasting, Splendid Dust of Ancient Suns, and Glory of a Far Dawn were able to escape in a Falco.

Builder ships were large Forerunner vessels commanded by the Builders. A single, massive Builder ship was at the center of the fleet spiral sent to retrieve the Didact on Erde-Tyrene

Forerunner cruisers were Forerunner capital warships. The cruisers were sufficiently powerful that four ships combining firepower were able to overwhelm the defenses of a Halo installation.

Forerunner mining ships were vessels used by Forerunner Miners. They were used to excavate and carry ore and minerals using an array of grappler, lifters, cutters, and churners on their undersides. They also possessed equipment that allowed them to thoroughly scan areas for useful minerals.[1] The mining ships were noted by Bornstellar Makes Eternal Lasting to be aesthetically displeasing to the extreme,[1] marking an unusual contrast with the pristine nature of other Forerunner architecture. However, it is possible that the Miners, being the lowest caste in Forerunner society, were not afforded the same resources to build their ships as the other castes. At least one mining ship was deployed to Earth in approximately 100,300 B.C.E. by Bornstellar's surrogate family in an attempt to find him. However, the search was soon abandoned either due to the bafflers surrounding Djamonkin Crater or to the area's sacred nature

Picket cruisers were small vessels used by the Forerunner Navy for orbital patrol and interdiction. Several of the cruisers were able to fit inside Didact's ship.

Fortress-class vessels, more commonly known as fortresses or fortress ships, were massive warships used by the Forerunner military.[1] Fortress-class warships were some of the largest and most powerful vessels in the Forerunner navy. From bow to the ships were approximately 50 kilometers long and were 10 kilometers across at the widest point. A single fortress ship can carry thousands of support craft. The hull is divided into three sections: the foremost section of the ship is a massive hemispherical structure 10 kilometers in diameter. The dome's hollow core serves as living space for hundreds of thousands of Forerunner Warrior-Servants. Below the dome is a mid-section composed of layered platforms supporting landing bays and weapon mounts. The aft section of the ship is a long "tail" covered in gun emplacements and other forms of energy weaponry. Fortresses were capable of deploying hundreds, if not thousands, of orbital picket cruisers, weapon-ships, and fast attack runners.

Weapon-ships were small remotely-controlled craft deployed from Forerunner fortresses. They were heavily armed, and could be controlled at a ratio of a million ships per warrior.

Fast attack runners were small craft deployed from Forerunner fortresses.

Planet-breakers were large Forerunner warships. They were able to carry over five thousand warriors and hundreds of war sphinxes, as well as armed scout craft and orbital picket cruisers. The Didact's ship was a planet-breaker.

Preservation-class escorts were escort vessels used by Builder Security. The escorts were used on Janjur Qom during the battle on the planet

The Keyship[3] is a classification of supra-luminal Forerunner naval vessel in use at the time of the Forerunner-Flood War. Mentioned in the hidden Terminals found on the Ark and Installation 04B, Keyships were a class of Forerunner vessel capable of activating portals leading to the Ark. They were capable of remote detonation to prevent their usage by the Flood. Though many more once existed, the majority were destroyed by the Librarian to prevent the Flood from reaching the Ark.

The Dreadnoughts are warships that were used by the Forerunner Navy. They are designated as dreadnoughts, though they should not be confused with the Forerunner Keyships.[1][2] The planetside docking towers for these ships can detach from the ground and hover above the surface of a planet. In space combat, the ships are capable of arranging themselves into a octagonal formation, from which thay can combine their weapons into a single blade-like beam. This beam can split other vessels in half.[2] These warships were common during the Forerunner-Flood War, when they were used widely in combat.[2] Among numerous docking facilities around Forerunner-controlled space, some of these ships were docked at the Apex Installation on a Flood-controlled Shield World. During the Human-Covenant War in 2531, the High Prophet of Regret and Arbiter Ripa 'Moramee went to the Apex to gather a massive and powerful invasion fleet for the Covenant Navy. In order to release the locking mechanisms holding the ships in place, they needed a Reclaimer. Thus, they abducted Professor Ellen Anders to activate it for them. The ships were destroyed when the artificial star inside the Shield World went supernova after the crew of the UNSC Spirit of Fire used their ship's Slipspace drive as an improvised bomb.

Sentinels

Enforcers are large Sentinel-like machines equipped with energy shields and an array of powerful weapons. They serve as part of a Halo Installation's defense against mass Flood outbreaks, and have been seen guarding key locations such as the entrances to the Sentinel Wall and the Library on Installation 05. Enforcers are produced by hovering Sentinel Production Facilities.[1][2] Enforcers have three Energy Shields; the larger two are split in half (for their guns to fire through), and the small upper shield protects the 'eye' of the Enforcer. The shields only protect the front side of the machine. Enforcers are armed with Pulse Beams and Missiles. They are also equipped with large claw-like arms which are able to pick up and rip apart most vehicles, resulting in death of all occupants riding in the vehicle.

Built contemporaneously with the construction of the Halo Array, Aggressor Sentinels were utilized as all-purpose workers and guards on Forerunner stations. Following the construction of the Halo Installations, Sentinels were reconfigured to be the first line of defense against Flood outbreaks and other external intruders. The mechanical nature of the Sentinels make them ideal combat units against an enemy that could convert conventional biological infantry into biomass - by deploying the Sentinels en mass, the Forerunners could battle the parasite without contributing to its numbers. Controlled by their own basic AI functions, as well as their Installation's Monitor, Sentinels patrol the Halo rings tirelessly and attack as their protocol demands.[3] When not in combat Sentinels serve as basic repair, maintenance and security drones for Forerunner installations and facilities where Flood samples are kept, working in conjunction with Constructors and Enforcers to ensure that the facility remains in working order. Sentinels are viewed by the Covenant as "Holy Warriors of the Sacred Rings,"[4] machines meant to be worshiped and respected by all who believe in the path.

Sentinel Majors are similar to a regular Sentinel in basic shape and function. Sentinel Majors, however, are gold in color rather than silver, have stronger blue beams rather than weaker orange beams, are protected by a light energy shield, and fire more accurately. They were only observed on Installation 05 during the Battle of the Quarantine Zone. In the game, they are seen combating Flood and the Covenant. Sentinels have been known to have been created long before Alpha Halo was ever conceived. They operated automated facilities such as Gas Mines, like the one found on Threshold for untold centuries before the facility was redesigned to research the Flood. Therefore it is possible that they were only outfitted for combat after the Flood was discovered.

The Onyx Sentinel shares a vaguely similar appearance to a Monitor - a round metallic sphere a quarter meter in diameter, with a central "eye" that glows golden. Hovering around this sphere are three meter-long cylindrical spars or "booms", which are suspended in midair at equidistant points around the sphere. These booms could change position for various purposes, and would rapidly "pop" into place to form a triangular plane when the sentinel's shields were active. The central eye is the weaponry and offensive capability of the sentinel as it charges and unleashes what appears to be a devastating array of energy. The Onyx Sentinel also has anti-gravity technology, similar to that of the Monitors. The Onyx Sentinel can even reach escape velocity and fly into outer space; in ground operations, it normally engages its targets at a height of three meters, working a "Higher Ground" battle mentality. It is also able to attenuate its booms to the various signals, such as that of UNSC COM channels. The sentinels are also equipped with Forerunner translation technology and can actually speak the Human archaic language and root language of Latin. The Onyx Sentinel is infamous to be the most dangerous classification of any known Sentinel, is extremely versatile, and is a powerful combatant on both the ground and in space. One of their primary advantages, is a gold-colored Energy Shield that is entirely resistant to all projectiles, even the rockets of the SPNKr Launcher and LOTUS Mine detonations; however, the motion sensors that activate the shield are duped by slow moving objects, such as a rock, which was used to destroy one Sentinel on Onyx. It is unknown why the shields only snap into place when fast moving projectiles are coming in the direction of the Sentinel (it is unlikely that they do so to conserve energy, for the enormous output of energy per beam is, presumably, far greater than the amount used to hold shields in place), but it's possible that it has flaws in its sensors, and objects moving at slow enough speeds can be virtually invisible to it. It is also very adaptive, each Sentinel transmitting its combat footage to an unknown intelligence that continually upgrades Onyx Sentinel combat algorithms. As per a Spartan: "We are teaching it how to fight." The Onyx Sentinels can also merge together for a variety of purposes, such as combining to increase firepower and shield strength, architectural purposes, and forming clusters to protect Onyx. Even a pair of Sentinels is exponentially more dangerous than a lone one, as a pair, unlike individual Sentinels, can activate its shields and fire its energy weapon at the same time. It is far superior to the regular Sentinels that guard the Halo installations and The Ark and even the Sentinel Majors of Installation 05 due to its shielding and extreme firepower. Onyx Sentinels fire golden, lethal beams of energy from a central eye, which is thought to be similar in strength to the beam weapon fired by 343 Guilty Spark at several points of Halo 3 when the player is on the Ark, not just fighting him at the end. This attack causes devastating damage: the destruction of a granite plateau, vaporization of a combat bunker, and the instantaneous destruction of any ground vehicle or infantry, even including a SPARTAN-III. Enough Onyx Sentinels (about forty-five) can even vaporize a large starship with apparent ease. Onyx Sentinels are also known to have other specific tasks beside combat, much like other types of Sentinels. Because of their modular shape, they can transform into several different types of configurations. For example, they can interlace into oblong-shaped formations, which are used for excavating and earth-moving. In the center of the worm-shaped configuration travels a continuous stream of stone. This type of configuration has been observed excavating the underground Forerunner city on Onyx, to allow access to the Shield World within. These variants are not hostile, unless provoked. Another, more original role of the Onyx Sentinels was making up the entire planetary structure of Onyx. Under the artificial and entirely terraformed surface were trillions of these machines, forming the megastructure. In the end of the battle of Onyx, as the portal to the Shield World closed, the artificial planet dissolved with the sentinels decimating a Covenant fleet. It is unknown if they rearranged to form the planetary structure after this.[1] To maintain the sentinel population of Onyx, the artificial planet had a massive Sentinel Production Facility that produced a new Onyx Sentinel every six seconds.

Constructors are small flying machines built by the Forerunners. Their only function is to repair Forerunner structures that appear to be damaged. They can only be found on Forerunner worlds. Sentinels will come to their aid if they are attacked, as they have no weapon systems of their own to defend themselves. The Construction Beam is fired from the top half of the Constructor, however the constructors on The Ark fire their beams from the bottom. Sentinel Constructors also play another role as a security grid. When a Constructor is attacked, an unknown signal causes the Sentinel Launchers to begin deploying Sentinels. Constructors form an excellent security perimeter. Constructors are devices similar to Sentinels in design, that mainly repair damage to any Forerunner structure they can find, using weak energy beams similar to Sentinel Beams. The beams are small and blue, and are harmful if they come into contact with an organism. This is unknown whether they will harm the Constructor itself, though. The Sentinels will come to their aid if they are attacked, as they are ill-suited for combat, having no weapon systems of their own; however, their beams will damage you if you get caught in the path (on Legendary difficulty their beams can kill in seconds). They also use their beams to lower the shields on Pistons, allowing them to move throughout the Sentinel Wall quickly

The Guardian was a Forerunner Sentinel located at the Ark.[2] They bear a strong resemblance to the S'pht Compilers from Marathon and the Forerunner hologram in Epitaph. The Guardian Sentinel was originally set to appear as a fighting enemy in a campaign level that later became a multiplayer level Guardian but was removed, and featured in The Art of Halo 3 instead. It was stated that the player would have been able to rip out the Guardian's eye beam and use it as a weapon in the campaign level.[3] Although this Sentinel was cut from Halo 3, two Guardians are seen escorting a Keyship to The Artifact in Origins.

Protector Sentinels are smaller, faster, and occupy less of the population limit in Halo Wars. It is in the support role that they excel - their Y-button ability is to attach themselves to one of the player's other units, following it in action. Only one can be attached to a single unit one time. The Offensive Protectors are the only Protectors that can be used as a standard unit, because they can attack without being assigned to a squad. In direct combat, they are less effective than standard Sentinels. However, similar to the Sentinel Majors, they are equipped with an onboard beam weapon which fires a single blue colored beam. They are of similar shape to the Super Sentinel and are slightly bigger than Constructors. They have several laser target systems that scan for any threats. Offensive Protectors are the only variant in the Campaign of Halo Wars. The Healing Protectors and the Shield Protectors are the about the same size as Offensive protectors, smaller than a standard Sentinel but larger than a Constructor. Unlike the Offensive Protectors, both variants do not possess guiding lasers. The Healing Protectors and the Shield Protectors are identical in shape; Healing Protectors differs from Shield Protectors as they radiate a green aura. Shield Protectors have the ability to form a protective shield around its host, similar to the Halo 3's Bubble Shield whereas Healing Protectors have the same ability as the UNSC Marines with the Medic Upgrade, meaning they heal the squad after combat.

The Retrievers was a Forerunner Sentinel variant. They were designed to strip mine the resource moon located in the middle of Installation 00[1], to help in the construction of a Halo ring, such as the newly constructed Installation 04 as seen in the Halo 3 levels The Covenant and Halo, and were also used with the construction of the Portal on Earth, in the present-day country of Kenya [2]. One of the concepts for the multiplayer level Blackout had the map set in the partially destroyed insides of a Strato-Sentinel orbiting the Ark's strip mining moon.

The Super Sentinel is a variant of the basic Sentinel design, but considerably larger. They are available as a support unit in Halo Wars. They, like regular Sentinels, are built at the Sentinel Shop. Intended to support anti-vehicle and anti-infantry operations, they are unable to engage aircraft, and require regular Sentinel escorts for aerial protection.[1] They cost 250 resources and require a minimum tech level of 2 to be produced and count as 2 population. They fire a beam of energy that temporarily prevents an enemy ground unit from attacking and reduces its movement speed. However, the beam does not do much damage by itself.

The Obelisk Sentinel was an extremely large Sentinel-like machine used by the Forerunners during the Forerunner-Flood War. It is the largest Sentinel variant observed to date, dwarfing the Strato-Sentinel in comparison. Its armament includes an extremely powerful energy weapon, capable of firing a lightning-fast energy beam at long range and producing an explosion powerful enough to level entire cities.[1]

Gatherers are Forerunner machines whose primary function is to gather specimens of different species and to transport them for study and cataloging. So far, these machines have only been observed operating from Line Installation 1-4 on an Unnamed Moon.[3] Gatherers consist of a fairly large main body with three red eyes and a holding tank for captured specimens on their backs, filled with a purple liquid. They have eight tentacle-like clawed arms, two much smaller arms, and four legs, although they are usually seen floating through the air. Gatherers are armed with an energy weapon similar to, though more powerful than, the Sentinel Beam, located below the tentacles. Much like the Sentinel Beam, the weapon can be detached and used as a hand-held weapon.

The Assembler is a type of Forerunner Sentinel. Like the similarly named Constructors, Assemblers are likely used to build and maintain Forerunner installations. Though they are not designed for combat, they will suspend their primary duties to engage Flood forms in the event of an outbreak.

The Promethean Watcher is a Forerunner Sentinel variant. Like other Promethean constructs, the Watcher was designed as a countermeasure against the Flood. Numerous Watchers were encountered on the shield world Requiem in summer 2557. Watchers are typically deployed from the armoured carapace of their Promethean Knight Commanders, assisting them with aerial combat screening and often forcing opponents to engage the Sentinel first. The Watcher is capable of healing and augmenting damaged allies, providing them with hard light shields, and can catch and return enemy ordnance, such as grenades, with a gravity-displacement field. They are also capable of summoning Promethean Crawlers to the battlefield by conjuring the Crawlers' forms from raw material in the ground. They are armed with a Boltshot, apparently built-in. The Watchers also can resurrect Knights killed in combat. Unlike the angular, blue-lit appearance of most Sentinels, Watchers have curving carapaces with orange lights. They have a number of appendages, including what appear to be legs hanging below the midsection and two large disks on both sides. Most of these segments lack physical joints and are held together by energy fields. Above the midsection there appears to be a head with stylized facial features.

Other Constructs

Vigilants were tiny Forerunner probes capable of entry into slipspace. Trillions of vigilants were used to form the Quarantine Shield around Janjur Qom by constantly weaving in and out of slipspace around the planet.[1] In this way, they could presumably monitor both slipspace and ordinary space simultaneously.

Armour Cracking Units are small Forerunner automatons designed to break through Forerunner body armour, usually for the purpose of sabotage. They are about the size of a human fist, and have been said to resemble metallic fleas. Armour cracking units were employed during the conflict on Installation 07, where they infiltrated ships and sabotaged the armour of the Forerunner combatants within.

Engineering Units were small Forerunner machines capable of automatically rendering repairs on damaged ships and equipment.

Promethean Knights are a class of mechanized Forerunner Promethean warriors. Several legions of Knights represent the central occupying force in the shield world of Requiem, alongside a number of other Promethean machines. The origins of these automatons are both ancient and mysterious. While they differ significantly from the ancient Forerunner Prometheans, a legendary class of Warrior-Servants, they are nonetheless a force to be reckoned with. They are fully weaponized, heavily armoured bipedal warriors, easily capable of engaging and terminating perceived threats in almost all environments. They are known to use Lightrifles and Scattershots as their ranged armament, in addition to a bladed weapon on one hand. They are able to deploy Watcher drones, carried in the back of their armoured carapace, for combat support. The Watcher sentinel can greatly improve the Knight's combat capabilities, raising hard light shields or healing the Knight, summoning Crawlers, or flinging back enemy grenades or other ordnance. Some subtypes also make use of autosentries in addition to the support that they can already summon. Upon taking critical damage, Knights completely disintegrate; their bodies erode away from where the fatal shot was received and dissolve into glowing particles. Despite this, they can be recreated and revived on-site by a Promethean Watcher. Knights have two sets of arms; two large, artificial arms at each shoulder in which the weapons are mounted and two smaller arms below the shoulders. The larger arms are composed of separate segments held in formation through an energy field. Knights also have a comparatively smaller set with small, five-fingered hands. These smaller arms are more "organic" in shape and are physically attached to the Knight's body. Knights are covered in patterns of light and have a fire-like glow around their heads. The head features an armoured helmet with glowing eyes and what appear to be grimacing jaws with rows of teeth. This helmet assembly can be retracted in two sections, revealing a glowing humanoid skull underneath.

Knight Lancers are a class of the Promethean Knights encountered by the UNSC on the shield world Requiem in late 2557. Lancers are primarily used as scouts and marksmen, as well being extremely accurate from great distances. Lancers are known for using Promethean vision to track targets, even if they are behind solid objects. Lancers are capable of teleporting over short distances; this ability allows them to enter the battlefield via teleportation or to quickly retreat during battle. Lancers are also capable of charging at their opponents in a zigzagging motion at an incredible speed. This enables them to make use of the Scattershot's effectiveness in close quarters.

Knight Battlewagons are a class of Promethean Knight encountered by the UNSC on the shield world Requiem in late 2557. Battlewagons are heavily armed and armoured, serving as a last line of defense when other forces have failed. They are equipped with hard-light shielding, and are capable of deploying autonomous sentries. They use Scattershots for close-quarters combat.

Knight Commanders are a class of Promethean Knight encountered by the UNSC on the shield world Requiem in late 2557. Commanders have similar combat skills of standard Knights but instead, lead and command groups of Knights into battle. They possess stronger armour, deploy floating Autosentry turrets, and usually wield Incineration cannons.

The Crawlers are a form of autonomous Forerunner defense construct, designed by the Promethean Warrior-Servants as a means of asymmetrically combating the Flood. Crawlers are small, quadrupedal machines capable of both ranged and close-quarters combat, using a built-in Boltshot as their primary weapon; this weapon disintegrates targets to prevent their biomass from being co-opted by the Flood. Unlike the majority of Forerunner automatons, they appear to lack anti-gravity capabilities of any kind. Crawlers are ferociously aggressive, having been specifically designed to hunt down and eliminate any foreign threats, their inorganic nature making them immune to Flood infection. They travel in large packs and work together to destroy enemies by overwhelming them from every conceivable angle, relying on skirmishing tactics. Crawlers are often directed by Promethean Knights, who regard them as cannon fodder. They are protected by Watcher Sentinels, which can create new Crawlers from raw materials in the ground. In addition to the basic type of Crawler, a more heavily armed unit and a long-range unit are also employed. Numerous Crawlers were encountered by UNSC Defense Force and Covenant personnel on the shield world Requiem in summer 2557.

Crawler Snipes are a class of Promethean Crawlers encountered by the UNSC on the shield world Requiem in late 2557. Crawler Snipers appear to be more armoured than the standard Promethean Crawler and are armed with a built-in Binary Rifle.

Alpha Crawlers are a class of Promethean Crawlers encountered by the UNSC on the shield world Requiem in late 2557. Alpha Crawlers lead packs of lesser Crawlers. They are distinguished from other Crawler subtypes by the array of glowing spikes on their carapaces, and are armed with a built-in Z-130 Suppressor.

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