The Protheans are an extinct alien race which mysteriously vanished over 50,000 years ago. The Protheans arose from a single planet and developed an immense galaxy-wide empire encompassing many other spacefaring species. Not much is known about them, but many of their artifacts, ruins and technology have apparently survived the ages. The Protheans have been credited with creating the Citadel and the mass relays, feats of engineering that have never been equaled and whose core mass effect field technology forms the basis of contemporary civilization. Prothean artifacts, therefore, have immense scientific value and are seen to belong to the whole galactic community.
Protheans are an anthropoidal race. They have two pairs of eyes with each eye possessing dual pupils, and two pairs of nostrils. Their heads are covered in a thick, layered carapace that gives them a distinctive shape. The skin surrounding this carapace is a pale blue-gray color mottled with muted yellow spots, but their hands each have three fingers, and their feet each have two widely-spaced toes.
A unique attribute of Prothean physiology is an experiential exchange system based on physical touch. By touching something or someone, a Prothean could recall its experiences. This system can transfer complex ideas, with a Prothean being capable of learning a new skill or foreign language with a single touch. This sensory mechanism arose because the Protheans evolved as hunters and needed to be thoroughly aware of their environment. This is similar to the idea of psychometry.
From the few specimens of Prothean genetic material that have been found, modern scientists have learned that Protheans have a unique "quad-strand" DNA structure. It has also been hypothesized that Protheans were resistant to low levels of radiation because of the discovery that Prothean comm towers produced small but significant amounts of ionizing radiation, enough to damage the DNA of Earth creatures such as fruit flies and bees.
Forging an Empire
Very little is known about the origins of the Prothean race. After achieving spaceflight, the Protheans discovered the ruins of a previous spacefaring race, the inusannon, and from those ruins learned about mass effect physics and developed FTL technology. The Protheans would expand throughout the galaxy with the help of the mass relay network and make the Citadeltheir capital.
Eventually, the Protheans faced a hostile machine intelligence which threatened to overwhelm them. To defeat the machines, the Protheans decided to unite all of the galaxy's sentient organic life under their empire. Organic races that resisted the Protheans were soundly crushed. In time, each of the servant races assimilated into Prothean culture and came to think of themselves as Prothean. The Prothean Empire held its own against the machines in a conflict known as the "Metacon War".
At some point the Protheans learned of the existence of the Reapers and their cycles of galactic destruction through studying the ruins of other extinguished civilizations. Several countermeasures were devised, including the Crucible, which was based on designs left behind by previous civilizations. In the event that the Reapers prevailed, the Protheans also began extensive observation of primitive species such as the asari, hanar, humans, salarians, and turians; it was hoped that some Protheans would survive the Reapers' purge and go on to unite these species to create a new empire.
The Protheans' belief that they could hold their own against machine intelligence was shattered with the arrival of the Reapers, who were far more advanced than the machines the Protheans had been battling. Even though the Protheans already knew of the Reapers, they were nonetheless caught completely off-guard by the scale and rapidity of the assault. The Reapers entered the galaxy through the Citadel, instantly decapitating the Protheans' government and disrupting the mass relay network, isolating Prothean systems from one another. Worse, records on the Citadel provided the Reapers with access to all of the Protheans' census data and star charts, allowing them to effectively track every Prothean in the galaxy. The Protheans' greatest strength, their unified empire, proved to be their downfall. As the Protheans were united under the leadership of a single governing species with a series of subordinate races, the Reapers were able to quickly undermine the Prothean hierarchy and cause Prothean forces to become scattered when their ruling body had been compromised. On top of that, as all the races within the Empire conformed to a single military doctrine they proved unable to adapt and compensate for when the Reapers identified and exploited their weaknesses.
Over the next several centuries, the Protheans would fight the Reapers from system to system, world to world, and city to city. If necessary, whole colonies were sacrificed and abandoned to the Reapers; while the Reapers concentrated on subsuming the inhabitants of those colonies, the Protheans had time to regroup. In the long run, however, this strategy was extremely costly, depriving the remaining Protheans of whatever infrastructure and manpower they had given up. Inexorably, the Reapers conquered, enslaved, or destroyed Prothean-controlled planets. IndoctrinatedProtheans acted as sleeper agents for the Reapers, infiltrating and swiftly betraying their own kind and revealing the Protheans' dwindling hiding places and carefully laid plans to survive the destruction. Growing desperate, some Protheans made repeated offers of surrender, but these were always met with silence. Some Protheans believed that the Reapers could be controlled, but fell prey to indoctrination in their attempts to harness Reaper technology, sabotaging their race's attempts to destroy them with the Crucible.
After centuries of careful, systematic work, the Reapers had killed or enslaved every Prothean in the galaxy, and stripped their worlds of resources. Removing all traces of their presence, the Reapers then retreated through the Citadel into dark space and sealed it behind them.
As thorough as they were, however, the Reapers had overlooked a single world. The Conduit research team on Ilos, of which all records were destroyed in the initial attack on the Citadel, survived the first wave of destruction. The facility went dark in order to avoid detection and the staff agreed to go into stasis, hoping the danger would soon pass. Vigil, a VI, was assigned to watch over these Protheans in cryogenic stasis until the Reapers had gone, then wake the staff so they could begin to rebuild. But as the centuries passed and the Reapers persisted in their genocide of the Protheans, Vigil's power supplies began running low, and the cryo pods were in danger of failing.
Following contingency planning, Vigil began cutting power to the pods of non-essential staff to conserve energy. When the Reapers finally withdrew through the Citadel relay, only the top researchers — a dozen individuals — were left. Vigil woke them, and the scientists pieced together what had happened.
They soon realised the situation was dire. Without sufficient numbers to sustain a viable population, the Prothean species was doomed. Desperate for contact with others of their kind, a carefully-coded signal was sent to the beacons on other planets. Though it was unlikely there were other survivors, the scientists thought it was worth the risk to try reaching them. The signal not only contained a warning of the Reaper invasion, but a description of Ilos itself, to give them hope.
The surviving Prothean scientists knew that rescue was unlikely. Instead, they chose to protect the races they had been studying, spared destruction due to their lack of advancement, and began working out where the Reapers had come from, and how. After decades of study, they worked out the connection between the Reapers, the Citadel, and the keepers, and discovered a way to interfere with the signal that compels the keepers to activate the Citadel relay. Using the Conduit, the Prothean scientists left Ilos, travelled to the Citadel and altered this signal. Their intention was to prevent the Reapers from opening the Citadel relay again, and trap them in dark space, but they had no way to be certain their plan had succeeded. The fate of these Prothean scientists is unknown. As the Conduit portal only links one way and there was no food or water left on the Citadel, Vigil hypothesized they eventually starved to death.
Near the culmination of the next cycle, Vigil knew that the Protheans' efforts were not in vain when Commander Shepard's squad found Ilos. Sovereign had tried to signal the Citadel which would compel the keepers to open the relay to dark space, but thanks to the efforts of the scientists from Ilos, nothing happened. Vigil provided a data file to grant Shepard temporary control of the Citadel's systems, told Shepard all he knew of the Reapers and the Prothean extinction, and gave directions to the Conduit. When Sovereign was defeated and the Reapers' return to the galaxy was stalled, the Protheans' work finally succeeded, but ultimately this only bought the galaxy a short reprieve before the rest of the Reapers in dark space made their return.
While all evidence points to the Protheans being completely wiped out by the Reapers, this was not the case. The Reapers are believed to have attempted harnessing the genetic material from millions of Protheans to create a new Reaper. It is speculated by EDI that this attempt failed and so the Reapers decided to repurpose this substantial number of captive Protheans to suit the needs of the Reapers. Mordin speculated that these Protheans were indoctrinated and after a prolonged period of time as indoctrinated slaves, they were given cybernetic modifications to compensate for their growing lack of ability, which was a side effect of indoctrination. After several cloned generations, most likely during the centuries of Reaper genocide against the Protheans, the Reapers eventually decided to genetically rewrite these Protheans. These captives were transformed into an entirely new race which cooperated with the Reapers and would eventually be known to the citizens of the galaxy as the Collectors.
Being a rarely seen species whose existence was questioned by most, the Collectors resided in the Collector base, a space station located in the galactic core and only accessible through the Omega 4 Relay. Nobody had ever returned from a trip through the Omega 4 Relay and a Collector had never been examined, thus the Prothean/Collector link had never been discovered. Collector technology, while very advanced, no longer resembles Prothean technology, the species likely having developed on its own after the Reapers completed the genocide of the Protheans, also adding to the belief that the Collectors and Protheans are unrelated. The Collectors are presumed to have been left with partial access to Reaper technology, possessing Husks, a Reaper IFFwith which they could safely operate the Omega 4 Relay, and Reaper technology which protected the Collector base from the harshness of the galactic core.
For the next 50,000 years, the Collectors would periodically travel to the Terminus Systems and make efforts to acquire seemingly unimportant items or small numbers of very particular types of individuals from certain species in exchange for their advanced technology. Whether the Collectors were always acting as directed by the Reapers during this time is unknown and the reasons for these transactions were never revealed by the Collectors. Immediately after the destruction of Sovereign, the Reaper known as Harbinger began directing the Collectors in the abduction of what would have eventually been millions of human colonists as part of the Reaper plan to create a Human-Reaper, part of a renewed attempt to begin the next cycle of extinction. Shepard took a team to the Collector base and ensured that the Collectors were wiped out, aware of the fact that the Collectors were once Protheans. This possibly eliminated the last remnants of the Prothean race.
Ilos was not the only place where Protheans tried to survive in stasis. Nearly one million Prothean warriors and their commander, Javik, were stored in cryogenic lifepods in a bunker facility on Eden Prime. Javik's mission was to lead the warriors in rebuilding the Prothean Empire once the Reaper threat had passed. Before the facility could be sealed, however, indoctrinated traitors leaked its existence to the Reapers. Hundreds of thousands of stasis pods were destroyed in the attack on the facility, killing their occupants. To preserve the few remaining survivors, the facility's VI, Victory, initiated a neutron bombardment to purge Reaper forces. The bombardment also severely damaged the facility and rendered the systems responsible for automatically awakening the Protheans from stasis inoperable. As Javik's survival was a priority, Victory was forced to divert power from the remaining stasis pods to keep Javik's pod working as long as possible in the hope that future civilizations would discover it and revive him. Over 50,000 years after Javik entered stasis, Commander Shepard discovered and activated his pod. With his race destroyed and his mission failed, Javik believes his only purpose now is to wreak vengeance on the Reapers by joining Commander Shepard.
The Citadel was the Prothean seat of government, and the heart of their galaxy-wide empire. Although the Protheans were a single race, as they expanded and assimilated other spacefaring races into their empire, those servant races adopted the name "Prothean" for themselves as well. This assimilation was not always peaceful, as advanced species who attempted to deny or oppose their admittance into the empire were forcibly conquered and assimilated into Prothean society. The Protheans justified this cultural reconditioning by claiming that if the races who opposed them were actually stronger than the Protheans, then they would take the Protheans' place as the galaxy's dominant civilization. This ideology was also dictated by necessity. After the Protheans encountered hostile machine intelligences, they ultimately decided that all organic races should join together for the sake of survival.
The beacons and the Eletania ruins suggest that, like the asari, the Protheans were comfortable with the notion of transferring data to an individual's mind. They invested heavily in their scientific research, a policy that eventually paid off, if too late to save their own species. Prothean society was heavily regulated; Javik mentions that playing games of chance was an offense punishable by death.
Though the Protheans did not create the mass relays or the Citadel, they were still very technologically capable and scientifically curious. As well as studying developing races like humans and the hanar, they built a galaxy-wide communications network using beacons that transmitted information directly from mind to mind, and created data storage devices that still worked fifty thousand years later. They also developed a form of VItechnology and used cryogenic preservation techniques, which could help an occupant survive a neutron bombardment, as well as advanced architectural design and intricate holographic interfaces.
The architecture on Feros and Ilos shows the Protheans were able to build and maintain enormous cities and arcologies. However, given the fact that the Protheans were victims of the Reapers' trap, using their technology without knowing they would eventually be harvested as a result, much of Prothean architecture seems to have been influenced by structures like the Citadel, blurring the line between what the Protheans built and what they found. In addition, at least some of their cities - those of Ilos in particular - were built upon the ruins of a previous civilization, the Inusannon, which had been wiped out by the Reapers 50,000 years prior.
The Protheans were also skilled at creating kinetic barriers. They built elaborate mass-effect defense grids using barrier curtains and a kind of personal defense shield that acted like an energy bubble, surrounding and levitating the individual who activated it. While inside, the person was impervious to harm but helpless, similar to a biotic stasisfield.
Perhaps the single most advanced piece of technology developed by the Protheans was the Conduit, a miniature, prototype mass relay designed to reach the Citadel from Ilos. This was a feat unequaled by any known contemporary or precedent race; given the complexity of the relays and other Reaper technology, reverse-engineering a mass relay is believed to be extremely difficult.
While little is known of the Prothean military, it is known that they possessed fleets capable of defending their empire from threats. The flagship of the Prothean navy, Penumbra Apex, was equipped with a cannon similar in power to that of a Geth Dreadnought. Also, the Protheans produced Particle Rifles for their Infantry and had at least one Biotic near the end of the Reaper Invasion.
Various Prothean ruins still survive on planets like Feros, Quana, and Therum, as well as many known yet unexplored sites in the Attican Traverse, with more unknown sites believed to exist elsewhere throughout the galaxy. While these ruins are surprisingly intact for their age, many were plundered long ago with time and generations of looters having picked their dead cities and derelict stationsclean. Functioning examples of Prothean technology are rare.
While hunting for rogue Spectre Saren Arterius, Shepard discovers Prothean data discs and ancient ruins on some uncharted worlds; the commander can even receive a Prothean "trinket" as a gift from Sha'ira, but as Liara T'Soniclaims, solid evidence on the Protheans is scarce.
With the help of Shiala on Feros, Shepard also gains the Cipher, which is the key to fully comprehending the vision from the beacon. As the vision was meant for a Prothean mind, understanding it requires the individual to think like a Prothean - to understand their culture, biological instincts, history and ancestral memory. This "cipher" then allows the individual to unlock the true meaning of the images, and understand the vision as it was meant to be seen. According to Shepard, the Cipher's effect on the vision is quite subtle, and Liara's Prothean expertise is necessary to make sense of the images. The Cipher also grants Shepard complete knowledge of the Prothean language.
In addition to the technology they left behind, the Protheans left a greater influence through their in-depth study of other races. Their work has had the greatest impact on humans and the hanar. In humanity's case, the discovery of Prothean ruins on Mars, which were home to a small data cache, introduced humans to element zero and eventually revealed the location of the Charon Relay. A Prothean ruin on Eletaniacan also yield an ancient recording from a Prothean data recorder that was implanted into a Cro-Magnon human. The hanar, who call the Protheans "the Enkindlers", credit them with giving the hanar sentience and language, and worship them as an elder race who allowed them to become civilized.