The Citadel Supreme was first built by Supreme in 1939 when he came of age from being Littlehaven's protector to become Omegapolis' greatest champion. It was secretly constructed in space until it was completed and relocated into Earth's atmosphere in 1940 to be his base of operations. The citadel uses anti-gravity to stay afloat and produces artificial clouds to keep its location hidden from the rest of the world. The first design was more spherical in its primitive design.
The citadel was later rebuilt in 1964 after it was attacked by the combined forces of Darius Dax and Optilux. This time the citadel's design became a bit more luxurious and majestic. The key to access the citadel requires Supreme, or Suprema, to generate a hand-made bolt of lighting into a electro-sensitive "key hole" of sorts onto the front door of the building. The citadel is safely guarded by Suprematons, robot duplicates of Supreme, led by S-1.
Supreme does allow guests to visit the citadel upon his approval. Such visitors include Judy Jordan, Jonas Tate (the father of Lucas Tate), the Allied Supermen of America (Professor Night, Glory, Diehard, Mighty Man, Roy Roman, Doc Rocket, Alley Cat, Jack O'Lantern, Black Hand, Storybook Smith, and Waxman). He later allowed Billy Friday to visit his secret headquarters for inspiration for his next comic book for Dazzle Comics. Unfortunately, he was exposed to Supremium when he was unsupervised.
When Supreme "returned" from the revision after leaving Supremacy, he "rediscovered" the Citadel. Once he arrived Supreme discovered that S-1 created Suprematon versions of his friends (Judy and Radar the Hound Supreme) and family (Joe and Joanne Crane) when his master went missing in 1971. Once the truth was discovered, he re-programmed S-1 back to his original programming and deactivated the impersonating Suprematons.
It has implied that different incarnations of Supreme, including all their friends, family, and even certain aspects of the places the live and operate, including the Citadel Supreme, are mysteriously teleported to a idyllic limbo dimension called Supremacy.
The citadel has also been used for special occasions. On one occasion, the citadel's stadium room has been modified to house the Youngblood murder trial in the Judgement Day event. Another special occasion was for the marriage ceremony between S-1 (now called Telos) and the Judy Jordan Suprematon.
The citadel eventually fell when Darius Dax brought an army of dimensional duplicates from Daxia to lay siege to all Supremes from Supremacy. It is unclear when the "revision" occurred again if a new Citadel Supreme emerged. Especially in Supreme: Blue Rose.
Inside of the Citadel Supreme
While the outside surface appears like a castle, the lower levels are beyond imagination. Aside from private living quarters for Supreme, Suprema, and Radar, the citadel has its own hangar, workshop & storage, a special zoo that houses mythical creatures, an alien botanical garden, a rear observation platform, a souvenir gallery, a science lab, an armory, an art museum, a stadium, a study room, a special room that houses a lost civilization that was victimized by Optilux (The Prism World of Amalynth), and a special prison for Supreme's enemies called the Hell of Mirrors.