Prothean

The Protheans are an extinct alien race which mysteriously vanished over 50,000 years ago. The only known space-faring species of their time, the Protheans arose from a single planet and developed an immense galaxy-wide empire. Not much is known about them, not even by the asari, but many of their artifacts, ruins and technology have apparently survived the ages.

It is believed the Protheans created 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.

Origins
Very little is known about the origins of the Prothean empire. Various Prothean ruins still survive on planets like Feros, Quana and Therum, as well as many unexplored sites in the Attican Traverse, but many of the ruins have been plundered long ago.

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 Eletania can 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.

Remnants
After suffering a vision from a Prothean Beacon on Eden Prime, Commander Shepard later realises that it was a vision of the Protheans being destroyed by the 'Reapers', the name the Protheans gave to a race of sentient machines. Liara T'Soni, an expert on the Prothean extinction, explains that this fits with her discoveries. The Protheans were not the first race to be completely wiped out in a cycle of extinction, merely the most recent.

Liara also explains there is remarkably little archaeological evidence on the Protheans, which seems strange given their level of advancement and galactic empire. 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 claims, 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. Not surprisingly the Cipher also contains a complete knowledge of the Prothean language, allowing Shepard to understand it.

The Cataclysm
On Virmire, Shepard discovers from Sovereign that the Protheans did not build the Citadel or the mass relays - they simply found them, like the other races in Citadel space, and used the mass relays to expand their empire. Vigil explains later that the Protheans were researching mass relay technology and had developed a prototype relay, the Conduit.

However, at this point, the Reapers returned through the Citadel relay, to continue their cycle of extinction. Before they were even aware they were under attack, the Prothean government was killed and all communications were severed. With the Citadel, the Reapers had control of the relay network, and soon isolated 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.

One by one, the Reapers methodically conquered, enslaved or destroyed Prothean-controlled planets. As the Protheans scrambled to understand who or what was attacking them, they took in refugees from these destroyed worlds. However, these individuals had been indoctrinated by the Reapers to act as sleeper agents, who swiftly betrayed their own kind and revealed the Protheans' hiding places. The Protheans made repeated offers of surrender, which were met with silence.

After centuries of careful, systematic work, the Reapers had killed or enslaved every Prothean in the galaxy, and stripped their worlds of resources. They retreated through the Citadel relay into dark space, and sealed it behind them.

A Sanctuary
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 staff agreed to go into stasis, hoping the danger would soon pass. Vigil, a VI, was assigned to watch over the remaining 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.

However, the surviving Prothean scientists knew that rescue was unlikely. Instead, they chose to protect the races they had been studying 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 interfered with 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 hypothesised they eventually starved to death.

Aftermath
The fate of the Protheans turns out to be part of the reason Saren joined with the Reapers: "The Protheans tried to fight, and were utterly destroyed." Saren believed that if the Protheans had surrendered and allied themselves with the Reapers, they might have been spared.

Near the culmination of the next cycle, Vigil knew that the Protheans' efforts were not in vain when Shepard's squad found Ilos. He gave them a program that would give them temporary control of the Citadel's systems, and directions to the Conduit. When Sovereign was defeated and the Reapers' return to the galaxy was stalled, the Protheans' work finally succeeded. However, given that the rest of the Reapers still remain in dark space, their solution may have only bought the Citadel races valuable time.

Mass Effect 2
Mass Effect 2 reveals the fate of Protheans who had were enslaved by the Reapers and taken into dark space. When Commander Shepard and his team arrive at the Collector base beyond the Omega-4 relay, they discover that the Collectors are actually genetically rewritten Protheans, presumably under Reaper indoctrination. They have been distorted to the point where the Protheans and Collectors share only a single genetic trait.

When Commander Shepard and his crew either set a bomb or a timed radiation blast all remaining Collectors aboard the Collector base are killed instantly, including their leader, possibly eliminating the last remnants of the Prothean race.

Physiology and Culture
The beacon flashback and statues on Ilos show that the Protheans were humanoid in appearance, but with extremely long tentacle-like fingers, toes and 'beards'. The architecture on Feros and Ilos shows they 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, a lot 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.

It has been speculated that the Protheans may have had some influence on Earth throughout human history, particularly ancient Egypt. Evidence to support this includes the pyramid containment units found scattered on many planets that bear an unmistakable likeness to the ones found in Giza, despite the fact that the Protheans were destroyed tens of thousands of years before these structures were built.

The Citadel was the Prothean seat of government, and the heart of their galaxy-wide society (as it has been for all other races that came before and since). The beacons and the Eletania ruins suggest that, like the asari, they were comfortable with the notion of transferring data to an individual's mind. Little is known about Prothean society, but they are the only known spacefaring species of their time, which may be why they took such an interest in developing and studying other races. They invested heavily in their scientific research - a policy that eventually paid off, if too late to save their own species.

Technology
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 work fifty thousand years later. They also developed a form of VI technology and used cryogenic preservation techniques as well as advanced architectural design and intricate holographic interfaces.

The Protheans also had a knack for creating forcefields. 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.

Further, as evidenced by the Conduit, the Protheans were able to reverse engineer the mass relays to construct a prototype relay corridor, a feat unequaled by any known contemporary (or precedent) race.

Planets with Prothean ruins or development

 * Agetoton -- debris of aerostat colonies; likely had a population of more than 100,000
 * Antibaar -- ruins resembling those on Eden Prime
 * Binthu -- pyramid
 * Chasca -- pyramid and dig site
 * Eden Prime -- intact Prothean Beacon
 * Eletania -- ruins and intact Prothean data recording
 * Feros -- ruined planet-wide metropolis
 * Ilos -- destroyed city with surviving subterranean archives


 * Kahje -- small ruins, some likely submerged
 * Mars -- ruined observation and biosciences post
 * Omega -- mined-out and developed asteroid
 * Quana -- ruined planet-wide metropolis
 * Sharring -- likely mined for helium-3
 * Therum -- buried Prothean tower, possibly due to volcanic activity
 * Tuntau -- pyramid
 * Zafe -- likely mined for helium-3

-and many unspecified worlds in the Attican Traverse.

Trivia

 * The name "Prothean" may derive from the Ancient Greek words 'protero', meaning "earlier" or "former"; 'proto', meaning "primary"; and 'protean', referring to that which is changeable or adaptable. They also bear a strong resemblance to the mythological Titan Prometheus who gave fire to mortals, which enabled them to learn the arts of civilization (indeed, the Protheans certainly seem to serve that role in the mythology of the hanar, who refer to them as the "Enkindlers".)


 * The Prothean statues on Ilos bear a striking resemblance to that of the Space Jockey as seen in the movie Alien.


 * The Prothean pyramids apparently resemble the title object in The Sentinel, a short story by Arthur C. Clarke, which later evolved into 2001: A Space Odyssey. However the 'sentinel' in the story was a tetrahedron, whereas the structures in the game are square pyramids.