For canon information, see the Mass Effect Wiki page for the Citadel.
The Citadel is a massive space station historically located in the Serpent Nebula, once believed to have been constructed by the Protheans at least 50,000 years ago. First discovered in the current era by asari explorers, the Citadel is now home to over 13 million sapients, representing the majority of starfaring races. The station houses the Citadel Council and embassies, making it the de facto political capital of the known galaxy.
During the final days of the Reaper War, it was moved to Earth by the Reapers and positioned in a stationary orbit over London. The Crucible ended the war, but the Citadel stayed over Earth. Nobody has found a way to move it and nobody really tried as there are far bigger problems to take care of. However, the Crucible was undocked and moved to a undisclosed location.
The controlled Reapers repaired the damaged station to a large degree before taking on the relays, making the Sol relay a central hub within the mass relay network.
The Citadel is composed of six primary structures: the Presidium (which includes the Citadel Tower) and the five Wards.
The Presidium is a ring 7.2 kilometers in diameter, habitable in its closed interior, home to the majority of political and diplomatic agencies, as well as the station's wealthiest residents and commercial facilities providing for them. The Citadel Tower, housing the Council itself, extends along the station's central axis, connecting at its base to the Presidium via a lateral crossover. The Presidium maintains an artificial 20-hour day-night cycle.
- Antares is a small restaurant run by humans but widely popular among turians because it serves surprisingly good dextro dishes along with human cuisine, integrated with asari and salarian elements.
- The Battle of the Citadel Memorial commemorates those of the Citadel Fleet and allied navies who gave their lives defending the Citadel during the geth attack.
- The Iolla Water Gardens is a Thessian meditative garden, comprised of a network of platforms and pathways arranged around water fountains and features. The Elcor Unity statue is nearby.
- The Presidium Museum of Culture showcases art and cultural artefacts donated by Council-aligned worlds.
- Serene Fountains is a spa known for its exclusive hiring practices and high prices.
The five Wards are arm-like structures, each 44.7 kilometers long, housing the majority of the station's residents and businesses. They attach at their bases to the Presidium ring, and are habitable on their inner surfaces which, although open to space, are protected by environmental fields (in addition, many sealed buildings rise past the 7 metre ceiling of the Wards' atmospheres). Due to not being enclosed, the Wards have no day or night.
Bachjret Ward has a reputation for being somewhat boring and sleepy, as much as a space-borne multimillion-inhabitant city can be those things.
Kithoi Ward, although broadly comparable to the other Wards, is often seen as a somewhat more prestigious location (although obviously less so than the Presidium). It is home to Palaven Gardens, inspired by the great parks on Palaven itself. There is a food market nearby, with many great eateries in proximity to the gardens.
Shalta/Aroch Ward was named twice out of a linguistic quirk now lost to history. It is thought to possess a subdued and calm nature befitting residential development. The Systems Alliance also owns research and development facilities here.
Tayseri Ward markets itself as the cultural and artistic epicenter of the Citadel, and has nearly recovered all of its pre-war glory. The Eden Prime War of 2183, specifically the Reaper Sovereign's crash into Tayseri, inflicted long-lasting damages to the ward, resulting too in civil unrest. Reconstruction efforts were interrupted by the Reaper War, and the ward's heightened criminal activity didn't subside until the Systems Alliance established their forward command center in Tayseri.
Zakera Ward is dominated by volus, elcor and hanar interests, although the residential and commercial population is diverse outside of these groups; in the 2180's a human commercial zone was established in the Shin Akiba district.
As witnessed in the official Codex material.
The "undersides" of the Wards between the inhabited superstructures and impenetrable outer hull are called the Foundations. These dangerous areas are filled with life support systems and power plants. Officially, only the keepers are allowed in the Foundations. In reality, the Foundations are the slums of the Citadel, home to criminals, minorities, transients, and the occasional "stateless" exiles. Some stay in the Foundations of their own will. Others end up there when the opportunities they sought in the Citadel do not come.
The station's recycling systems are located in the Foundations. These manufacture a variety of artificial organic pastes that can be eaten for sustenance. They are free and nutritious but nearly tasteless and of unpleasant texture. Poorer Citadel residents quickly become adept at dressing up this bland fare with sauces and spices while imported foodstuffs are a popular luxury of the wealthy.
Threads of Interest
Citadel Elevators: Stories regarding this most infamous of station features.
Easier Solutions: As the Citadel and the Systems Alliance talk jurisdictions, CDN discusses alternatives: should the Citadel just be moved again, if possible?