For specific structures, see Citadel (Cardassia) or the Yolja Citadel. A citadel is a fortified building used for defense. Contents[show] History and specificsEdit On the planet Agena IV, the city of the Machs was protected by a citadel. (TOS comic: "The Expansionist Syndrome") AppendicesEdit See alsoEdit castle fortress (fort) ReferencesEdit TOS comic: "The Expansionist Syndrome" External linkEdit Citadel article at Wikipedia, the free encyclopedia. Retrieved from "https://memory-beta.fandom.com/wiki/Citadel?oldid=690430" Categories: Memory Beta articles sourced from comics Architecture Add category Cancel Save Community content is available under CC-BY-SA unless otherwise noted.