Citadel

The Citadel may refer to:
*Citadel (level) - One of the Halo 3 DLC maps.
*Covenant citadel - 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.
*The Citadel Skull achievement - Claimed by obtaining the Citadel Skull.