Prothean

The Protheans are an extinct alien race which mysteriously vanished over 50,000 years ago, placing their demise at around 48,000 B.C.

Beginnings
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. Various Prothean ruins still survive on planets like Feros, Quana and Therum, but many of the ruins have been plundered long ago.

The Protheans are known to have studied other races, mainly bipeds, as their curiosity towards other creatures like them was compelling, but 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.

Extinction
After suffering a vision from a Prothean Beacon from 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. She also points out that there is remarkably little archaeological evidence on the Protheans, which seems strange given they were such an advanced race. While hunting for rogue Spectre Saren Arterius, Shepard discovers Prothean data discs and ancient ruins on some uncharted worlds, 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.

At 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. They used the Mass Relays to expand their empire before the Reapers invaded and annihilated them. Vigil explains later that the Protheans were researching mass relay technology before they were attacked and had just developed a prototype relay, the Conduit. Before they even knew it, the Prothean leaders were killed. From the Citadel, the Reaper had access to all of the Protheans' locations and disabled all mass relays, isolating worlds from each other. One by one, the Reaper conquered or enslaved Prothean planets, having indoctrinated many individuals as sleeper agents who betrayed their own kind in refugee camps. By the end of the genocide, the indoctrinated either starved or died. Though the Reapers believed they had slaughtered or indoctrinated every Prothean across the galaxy, the Conduit research team on Ilos, whose records were destroyed in the initial attack, had managed to survive. Vigil was assigned to watch over the remaining Protheans in cryonic stasis until the Reaper invasion had passed, but the genocide took centuries and Vigil's power supplies began running low.

Following contingency planning, Vigil cut power to the pods of non-essential staff until only a dozen top scientific individuals were left. Without sufficient numbers for a viable population, the Prothean species was doomed to extinction. A 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 and find them, to let them know about Ilos and give them hope. Not expecting a rescue, the surviving Prothean scientists then tried to leave a legacy for the races they had been studying, breaking the cycle by traveling to the Citadel and interfering with the signal sent to the keepers. Their fate is unknown although Vigil hypothesised they starved to death on the Citadel, as the Conduit portal only links one way and there was no food or water on the station.

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 believes 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 -- at least, temporarily, for Shepard is well aware the rest of the Reapers will eventually return to the galaxy and is determined to find a way to stop them.

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 developed a form of VI technology and used cryogenic preservation techniques.

The Protheans also had a knack for creating forcefields. They built elaborate defence 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, a feat no contemporary Citadel species has achieved thus far.

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.

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). It is not known whether there were any Prothean biotics or not, but given their knowledge of element zero, it seems likely. 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.

Known Prothean-settled worlds

 * Agetoton
 * Chasca
 * Eden Prime
 * Eletania
 * Feros
 * Ilos
 * Quana
 * Therum

Trivia

 * Their name most likely comes from Prometheus, the Titan who stole fire for humanity's benefit in Greek mythology (hence, the Enkindlers).


 * 'Prothean' is the only species name that is properly capitalized - all other species names are considered common nouns and are not capitalized, other than the Reapers and the Collectors, though these are just a designations as their real names are unknown.


 * The Prothean statues on Ilos bear a striking resemblance to that of the Space Jockey as seen in the movie Alien (1979).


 * The Protheans are very similar to the Forerunners in the Halo trilogy