The Citadel is a gigantic space station that is home to the Citadel Council. It and the Mass Relays were created by the Reapers. After the disappearance of the Protheans, the Asari were the first to discover it. Shortly after the Asari discovered the Citadel, the Salarians then discovered it, followed by the Volus, who were the third race to arrive. The Turians then moved in and took a seat on the Council. More and more species began to discover the Citadel and as a result embassies began to be established. Now the Citadel is the center of communication for political interactions between the various races that inhabit the galaxy.
Though having been discovered for well over a millennium, some very interesting things about the Citadel are still unknown until the end of Mass Effect. There is no knowledge of what material the Citadel is actually made of. The master control center and the cores location are unknown, as is the actual age of the Citadel. Lastly there are mysterious creatures called Keepers that work on the Citadel. They are mute creatures who do not do anything but work on the Citadel, though the specific processes that they regulate are unknown. Any attempt the disturb or study the Keepers is against the law, as the Keepers are known to self destruct when somebody interferes with them.
The Citadel is located in the Serpent Nebula, near to the star known as The Widow. It is surrounded by a number of mass relays providing easy access to and from the rest of the galaxy. The Citadel itself is comprised of a central ring with five long arms stretching outward from it.
Upon the central ring is built the Presidium of the Citadel, where the offices and embassies of all galactic races are situated, however the Presidium also includes various commercial and recreational facilities such as shops, restaurants and other places of interest. Perhaps the most important structure of the Presidium is the Citadel Tower in the center, which houses the chambers of the Citadel Council and the main traffic control of the Citadel. The Citadel Tower is only open to officials and those with special clearance and is also the location of the platform upon which Citadel Council meetings take place. The Presidium is controlled by the virtual intelligence Avina and has foliage, ponds and fountains throughout. It operates an artificial day-night cycle where for six hours out of the twenty hour day on the Citadel the lights are dimmed and the holographic sky is darkened. Space ports are also located around the central ring allowing ships to easily dock with the station.
The Wards are the area built upon the five arms of the Citadel. The markets of the Citadel can be found in the Wards and the Wards are also densely populated with residential areas. The Lower Wards are the location of the offices and custody suites of Citadel Security Services (also known as C-Sec) who police the Wards. The Wards also include a nightclub called The Flux, a gentlemen's club named Chora's Den and a med clinic. Breathable atmosphere only exists for approximately seven meters above the ground of the Wards so the many skyscrapers that exist across it are vacuum sealed. Due to the lack of day-night cycle in the Wards commercial activity is ongoing and most residents sleep and work according to personal need, as opposed to time schedule. The Wards is also home to the Silversun Strip. It features the Armax Arsenal Arena, Shepard's personal apartment, the Silver Coast Casino, Castle Arcade, a bar and the Tiberius Towers.
All ships which come within a few thousand kilometers of the Citadel are classified as being under the jurisdiction of Citadel control, however if such ships are aggressive there are a number of lines of defense the Citadel can employ.
The very Serpent Nebula that the Citadel is situated in acts as a form of defense as it is very difficult for attacking ships to navigate through. The Citadel has its own fleet of ships, simply known as the Citadel Fleet which is constantly patrolling around the station to defend against attackers. The fleet is comprised of ships from all races of the Citadel Council but is primarily composed of Turian ships and is headed by the Asari Dreadnought Destiny Ascension. Reinforcements can also quickly and easily make their way to the Citadel via the many mass relays that exist around the station. The Citadel itself can close its five arms inwards for defensive purposes and its hull is extremely resilient to attack. On-board the station two hundred thousand C-Sec patrol officers handle all types of crime.
After the fiasco on Eden Prime the Normandy is recalled to the Citadel by Ambassador Udina to give a detailed report of what happened. The crew goes before the council and tried to prove that Saren Arterius was behind the attack on Eden Prime. Saren appears via holocrom and vehemently denies any charges, instead he blames the whole incident on Humans and accuses them of trying to cover up their own mistakes. He also takes the occasion to point out that humanity that his reinforces what he has been saying about their race all along; that their aggressive expansion needs to be stopped. He also brings up the personal history between Captain Anderson and himself and asks the captain if he is trying to get even with him. Having no proof the Council rules that Saren has not done anything wrong and all charges were dropped. Dejected, Commander Shepard and Captain Anderson scheme on ways to find evidence that would prove Saren’s involvement in the whole incident.
During the course of his investigation Shepard finds out about a Thug named Fist who is involved with Saren. After confronting him he learns that in exchange for a large amount of cash, Fist has set up an Ambush for a young Quarian named Tali who has information about Saren’s betrayal in the form of a voice recording between himself and Matriarch Benezia. In that recording he talks about the success of the attack on Eden Prime and a mysterious object called the Conduit that would help bring back the Reapers. Shepard helps Tali escape from the ambush and she agrees to help him against Saren by giving them the evidence. Shepard takes this new evidence to the Council and along with Ambassador Udina presents it. The overwhelming evidence gives the council little choice but to find Saren guilty and revoke his Spectre status. Udina demands that the citadel sent its fleets after him to track him down. However, the council denies the request and points out that a fleet cannot track down one man. Shepard interjects and says that he could do the job if he was given the authority. The Turian representative opposes the move saying that Humanity is not ready for this honor but Shepard points out that it was a Turian who broke the law, he relents and Shepard and the council makes him a spectre, a first for humanity.
Near the end of the game, the player learns that the Citadel is actually an inactive mass relay that is used by the Reapers and is connected to the Conduit. Every 50,000 years, a message is sent to the Keepers telling them to active the relay. The Reapers will then begin to pour through and take over. After annihilating every organic being in the galaxy, they pass back through the mass relay into dark space, making sure to deactivate the relay so another species can occupy the Citadel and be unaware of it. The final battle in Mass Effect takes place on the Citadel as the Reapers fight to gain control of the structure.
Mass Effect 2
In Mass Effect 2, Commander Shepard travels to the Citadel but arrives in the Zakera Ward, which is home to many shops. Shepard converses with either Council Anderson or Council Udina (depending on who they picked at the end of the first game).
Mass Effect 3
In Mass Effect 3, Commander Shepard can go to the Citadel to meet with old allies and help unite the galaxy. In the end, Shepard realized that the Citadel is part of the Catalyst.
Real-life theoretical citadel
The design of the Citadel in the Mass Effect fiction is actually based on a real-life theoretical design for a human space colony habitat, referred to by astrophysicists as the "O'Neill Cylinder".
Conceptualised by famous physicist Gerard K. O'Neill in 1976, the O'Neill Cylinder design describes two giant hollow capsules (5 miles in diameter, 20 miles long) that each spin constantly to gain their own centrifugal force, acting like gravity does on earth, pushing outwards from within.
While the classic O'Neill Cylinder design portrays a capsule made of 3 panels of inhabitable land, and 3 panels for simulating the sky; the Mass Effect Citadel has 5 panels, all made for inhabitable land.
- Rotation: 3.5 minutes per revolution
- Rotational Gravity in the Wards: 1.02 Earth
- Rotational Gravity in the Presidium: 0.3 Earth
- Total Length (Open): 44.7 km
- Diameter (Open): 12.8km
- Ward Length: 43.6km
- Ward Width: 330m
- Presidium Ring Diameter: 7.2 km
- Presidium Ring Width: 553 m
- Exterior Armor Thickness: 13 m
- Population: 13.2 million (not including the Keepers)
- Gross Mass: 7.11 billion metric tons
- Height of the Presidium Tower: 1047 m