Citadel The Citadel is the heavily defended headquarters of the Brotherhood of Steel in the Capital Wasteland in 2277 . It is built into and beneath the ruins of the Pentagon , the pre - War headquarters of the U . S . military . Located on the west end of Arlington Memorial bridge , northeast of Arlington Library , it initially consists of four interior sections . Background . The ruling council of the Brotherhood of Steel , based in the Lost Hills bunker in Southern California , decided to send a contingent of soldiers to the East Coast to recover any and all advanced technology from Washington , D . C . and The Pitt , as well as to investigate reports of super mutant activity . The Pentagon , as feared , was largely destroyed . However , its sub - levels remained intact and contained enough pre - War technology and weaponry to keep Brotherhood forces going indefinitely . But there was something else as well , Liberty Prime - a technological marvel that , if restored , could help the Brotherhood rebuild their strength and reputation which had both been steadily declining for years . The discovery was significant enough to earn Paladin Owyn Lyons a battlefield promotion to Elder , and a new directive from his superiors – to establish a new , permanent Brotherhood base in the Capital Wasteland and continue the search for any other advanced technology hidden in the capital ' s ruins . Lyons accepted his new post gladly and founded the Citadel , built into and beneath the ruins of the Pentagon . It was a fortress the Brotherhood of Steel desperately needed and one they rushed to fortify . Layout . Exterior . The Citadel is a large fortress with walls of stone and steel . It retains the shape which gave it its name , the " " Pentagon . " " It only has a single entrance : a large metal gate usually guarded by multiple paladins and one sentry bot . ( After the water purifier is completed and operational these guards no longer appear . ) A small corridor leads from the main gate to a door which provides access to the inner bailey . The inside is inaccessible until the The Waters of Life segment of the main quest is completed . Entry is scripted as part of the completion of this quest . Before then , the guard commander Paladin Bael will gruffly deny entry . Bailey . The fairly large bailey serves as a training and sparring area . Under the command of Paladin Gunny , new recruits practice various skills from unarmed combat to firearm usage . To this end , the bailey contains shooting ranges and other installations for combat practice . A large hatch in the middle of the courtyard connects to the laboratory , although it cannot be used as an entrance by the player character . The laboratory and A ring , sections of the buildings which surround the yard , can be accessed through doors opposite and next to the main entrance . There are several beds here for the player character and initiates to use . Citadel - A Ring . The A Ring is a small sector within the Citadel which can be accessed directly from the bailey . The entrance is on the right upon entering the Citadel . The A Ring contains the Lyons ' Den , the Great Hall , the Library and entrances to B Ring as well as the Citadel laboratory . The Lyons ' Den is the quarters of Lyons ' Pride while the Great Hall serves as a briefing room for high - ranking Brotherhood members and the Pride . This is where the Pride gathers and waits for new action orders . In the library , the Lone Wanderer can find the Vault - Tec terminal they need to consult as part of Picking Up the Trail . Another terminal reveals some background information on the Maxson family and various tidbits of information about the history of the Brotherhood . Another terminal contains information on a UFO that crashed shortly before the war and a plan to send mutant rodents to weaken China . Citadel - B Ring . The B Ring is another section within the Citadel which can only be reached from the A Ring via two doors in the back . It consists mostly of sleeping quarters for all Brotherhood of Steel members as well as a medical bay and the private quarters of Owyn Lyons and Arthur Maxson . Lyons ' unique laser pistol is in his safe in his private quarters . Squire Maxson ' s room contains a hackable terminal in which , among various children ' s stories and other personal entries , one can find reference to a Guns and Bullets magazine under the bed in the Lyons ' Den ( A Ring ) . The medical bay is home to Sawbones , a unique Mister Gutsy robot who is doctor of the Citadel , which Knight Artemis finds " creepy . " Citadel - Laboratory . The laboratory is the third sector of the Citadel , connected to both the bailey and the A Ring . It spans two levels and consists of the main working area , the armory and sleeping quarters for the scribe s . Various terminals with technical background information on weaponry are scattered all over the place . The lab is naturally the working place for most of the scribes , save those of the Order of the Quill . While they are conducting research on various fields such as threat assessment , weaponry and defensive technologies , their main focus is the work on Liberty Prime , a gargantuan pre - War robot which was the main reason the Citadel base was established . Scribe Rothchild , who is part of various main quests , is usually to be found in the area just in front of the robot , on the bottom level . In the vicinity of the robot dock there ' s also a terminal with progress information on the work on Liberty Prime which allows one to run a sound check . On the wall at the bottom level there is a digital map display from which the Lone Wanderer can extrapolate the location of the Vault - Tec vault s in the Capital Wasteland if they have not already found them . After Scribe Rothchild has used it to show the location of Vault 87 , the map markers will automatically be added to the Lone Wanderer ' s Pip - Boy 3000 . There is a graphical error in the location of Vault 108 between the Pip - boy 3000 and the vault map on the wall . The wall map shows it north of Canterbury Commons and the Pipboy shows it south of Canterbury Commons . The armory is located in an extra room on the bottom level and is run by Knight Captain Durga . She will trade with the Lone Wanderer if they have Elder Lyons ' permission , which is easily obtained . Inside the laboratory on the same floor entered from , there is a room to the east . The companion Star Paladin Cross is located in that room , along with a set of power armor in poor condition . Citadel armory . If the Lone Wanderer chooses to destroy the Citadel in Who Dares Wins , they will find a door leading to the armory within the crater and one on the far side of the circular path around the crater . This section is not to be confused with the regular armory located in the laboratory . Within this armory , there is a terminal describing several " incident reports " and a wall - safe ( unlockable through the terminal ) containing Callahan ' s Magnum . Appearances . The Citadel appears in " Fallout 3 " and is mentioned in " Fallout 4 " . Behind the scenes . " The Citadel " was the original name of the Cathedral of " Fallout " in early design documents ( like the ) , as it was also the name of a similar structure in Wasteland .