Citadel (disambiguation)

Were you referring to:
 * Citadel (Level), the upcoming DLC map from the Mythic Map Pack.
 * Citadel (Covenant), the Covenant structure used in Halo Wars.
 * Citadel (Forerunner), the Forerunner structure located on the Ark.
 * Battle of the Citadel, the last major battle to be fought in the Human-Covenant War.