Citadel

Citadel is an upcoming Halo 3 map that will be included in the Mythic Map Pack. No specific release date has been confirmed yet, however this map is expected to be released with Assembly, Sandbox, Orbital, Longshore, and Heretic in the Mythic Map Pack"...in early 2009. “Winter,” as they say." - Lukems in the 10/10/08 weekly update.

Skull

 * This map has a skull for the multiplayer achievements.
 * When found it unlocks the achievement, Citadel Skull.
 * It has an image on the skull that resembles the Citadel in the Campaign level, The Covenant.

Trivia

 * This map is rumored to be a Forerunner map because of the Forerunner symbol on the Citadel Skull achievement.
 * This map could be based on the end of the level The Covenant as where Truth, attempts to activate the Halos because it's called "The Citadel", but may be a re-modeled "Citadel" instead.
 * It is possible this map will not ship with the Mythic Map Pack in February.
 * This may also be another map similar to Construct, but due to the Shotgun Spree achievement, it may be more of a close-quarters map.
 * Citadel may be a remake of the Control Room or have some resemblance to it.
 * Rumors saying that Citadel is inspired by The Covenant