Citadel

The Citadel was an enormous space station located in the Widow system of the Serpent Nebula, serving as the capital of the Citadel Council and the unofficial heart of the region known as Citadel space. For thousands of years it was thought to have been built by the long-extinct Protheans, but it was in fact a creation of the Reapers, built as part of their cycle of galactic genocide. It was here that Commander Shepard confronted the schemes that threatened the galaxy, and here that the final battle of the Reaper War was decided.

Structure and layout#

The Citadel was a massive construct shaped like a five-armed ring, similar in outline to a pentagram. A central ring some 7.2 kilometers in diameter anchored five arms, each roughly 43.6 kilometers long, and the whole station measured 44.7 kilometers from tip to tip when open. Gravity was simulated through rotation, holding at a comfortable 1.02 standard gravities on the arms and a lighter 0.3 on the central ring. The station could close in on itself, drawing its five arms together into a long, armored cylinder roughly 45 kilometers in length, a configuration reserved for times of emergency.

The central ring housed the Presidium, a vast park-like complex containing the offices of the galactic government and the embassies of the represented species, along with shops, restaurants, and recreational facilities for its wealthy residents. The Presidium maintained an artificial twenty-hour day, dimming its holographic sky for part of each cycle, and was monitored by a virtual intelligence named Avina. At its center rose the Citadel Tower, which held the Council Chambers and the main traffic control for the station. The five arms, known as the Wards, formed the densely populated residential and commercial sectors, home to millions of residents drawn from across the galaxy and never resting, with commercial activity that rarely ceased. Below the Wards lay the Citadel Archives, a repository for artifacts and records of importance.

Discovery and the Council#

The asari were the first to discover the Citadel, in 580 BCE, soon after learning to use the mass relays. They were joined shortly by the salarians and then the volus, and as other species made contact or found the station independently they gained embassies and came under the jurisdiction of the growing Council. In time the Council came to comprise the asari, the salarians, and the turians. Strategically positioned at the junction of numerous mass relays, the Citadel rapidly became a hub of commerce and diplomacy, and was chosen to house the Council, cementing its place as the political and cultural center of Citadel space.

Even after thousands of years of occupation, much about the station remained unknown. Its precise age, the resilient material from which it was built, and the location of its core and master control unit all stayed hidden. The most visible of its mysteries were the keepers, mute insectoid creatures that maintained the station's vital systems and could be seen working throughout it, yet whose nature and origins few understood.

Defenses#

As one of the most important locations in the galaxy, the Citadel was protected by multiple layers of defense. The Serpent Nebula itself formed the first, its composition making it difficult for an attacking fleet to navigate and mount a concerted assault. The Citadel Fleet, a powerful task force composed largely of turian vessels but drawing ships from all the Council races, constantly patrolled the surrounding space, led by the asari dreadnought Destiny Ascension. Should an aggressor break through, reinforcements could arrive within minutes by way of the nearby mass relays. If an enemy drew close enough, the station could close into its armored cylinder, whose hull was strong enough to withstand days of sustained bombardment from the most advanced weaponry. Internal order was kept by the Citadel Security Services, a force of some two hundred thousand officers handling everything from customs to hostage negotiation, supported by turrets to ward off small craft.

The true nature of the station#

The Citadel was not built by the Protheans; they were merely the last race to make use of it before the asari arrived. It, like the mass relays, was a creation of the Reapers, built to facilitate their cycle of galactic genocide. The station was in fact a dormant mass relay leading to dark space, designed as an elaborate trap: when a harvest began, the Reapers could use it to strike at the heart of galactic civilization and leadership in a single devastating blow. The keepers were placed aboard so that the occupying races would never discover the station's key functions.

According to the Prothean virtual intelligence Vigil, the last Protheans of the previous cycle reached the Citadel through the Conduit in a desperate effort to break this pattern. They succeeded in sabotaging the trap, though it came too late to save their own people; because the Conduit linked in only one direction, the Prothean scientists are thought to have starved on the station, unable to find food or water. Their intervention forced the Reapers to enter the galaxy by slower faster-than-light travel rather than through the relay network.

The Reaper War and the Catalyst#

At the height of the Reaper invasion in 2186, the species of the galaxy united to build the Crucible, a superweapon of ancient design intended to destroy the Reapers. Its final and most important component, the Catalyst, proved to be part of the Citadel itself. When this was discovered, the Reapers seized control of the station and moved it into orbit around Earth to protect it, sealing its arms and trapping most of those still aboard. With the Crucible unable to dock at the closed station, it fell to someone to reach the Citadel and open its arms manually.

During the battle for Earth, Commander Shepard boarded the Citadel through a transport beam and reached its controls. There Shepard encountered the Catalyst, revealed to be the intelligence that directed the Reapers, and was presented with a final choice over the fate of the galaxy. Depending on Shepard's decision, the Crucible's energy was released through the now-open Citadel and transmitted across the mass relay network. In some accounts the relays and the station were severely damaged and later rebuilt, in others the Citadel was left largely intact while the relays suffered; in every case the choice made aboard the Citadel shaped the galaxy that emerged from the war.