Citadel

Overview
The Citadel station is a massive space station constructed millennia ago by the Protheans in the heart of the Serpent Nebula. It serves as the home of the Citadel Council, a powerful multi-species governing body.

History
The exact date the station was created is unknown, but it was built by the Protheans sometime before their species went extinct 50,000 years ago. The next race to discover the Citadel were the Asari approximately 47,300 years later. In the meantime, the station was maintained by it's mysterious denizens, the Keepers.