Citadel

"In the heart of this Forerunner structure, far above the troubled surface of the Ark, another battle rages."

- Bungie

Citadel is a Halo 3 map that was released on September 22, 2009 with Halo 3: ODST, as a part of the Mythic Map Pack. The Shotgun Spree achievement is attainable on this map. The map is a section of the structure first seen in the Halo 3 Multiplayer map Epitaph, which is a Forerunner "cathedral" that towers over the Ark.

Design
Citadel is based off of the ground floor of the shield towers from the Halo 3 campaign level, The Covenant (Level). It is built off of the geometry from the area around the elevators. There are differences in the geometry for multiplayer game play reasons, including the removal of the automatic doors and minor adjustments to the terrain.

The outside of the map is the same desert from Epitaph as it is a part of the same tower. However the player cannot see the tower from the map as it blocks the view. The inside of the map is symmetrical, having identical bases and walkways, making it an ideal Team Slayer map. The textures of walls and floors resemble the textures of the walls and floors from Construct and The Covenant.

Citadel has a number of tight corridors and doorways, making grenade throwing much more frequent. The bases have two levels, with the top level accessible by a ramp or a nearby jump. The bases are also open, but still small, and have a wide open view over to the enemies base.

Strategies

 * There are many angled walls in this map, making grenade an ideal choice when going into an area unsure if enemies are there or not.
 * It is best to have your team secure the weapons available to them early in the game, as the other team has almost as easy access to them.
 * Considering the small nature of this map, a Power Drain is ideal for flushing enemies out.
 * It is possible to jump to the other teams base off of the rocket platform, this is especially good for Capture the Flag matches and Assault.
 * This map focuses incredibly on teamwork due to its tight corridors and open bases. Moving in groups provides a substantial advantage.

Achievements
This map has a Skull for the Multiplayer Achievements. When found, it unlocks the achievement Citadel Skull, which is depicted by the skull and a Forerunner glyph on the forehead. The skull is near the blue side of the map; near the area where a doorway is in between two glowing "B"s. The skull is on top of the "B" on the right hand side. It is hidden atop of the B inside a small concealed place. Another achievement for Citadel is Pull, given to the player for getting a shotgun spree on the map, worth an overall 25 Gamerscore. A great way to get Pull is to play Action Sack and try to get 2Flag Shottys.

Trivia

 * It has been confirmed this map takes place in the same tower-like Forerunner structure as Epitaph.
 * The map was first designed to be much bigger and originally had an elevator for each team, though these features have been removed for undisclosed reasons, most likely to reduce possible lag or eliminate possible glitches associated with such features.
 * The map has a cross-shaped symbol similar to the symbols on Sandbox and Sandtrap.
 * Previously, the game developers mentioned the map being larger as well as featuring "elevators". The reason for this is that the map is actually an almost complete replica of the ground floor chambers of the "Shield Towers" from, The Covenant (Level). In addition, if elevators were present they would have most likely been located in the maps center on the platform much like it had been in the campaign level with the second level of the elevators being the "shield control rooms" like the ones seen in the campaign.
 * The strange roaring noises heard on Chiron TL-34, Assault on the Control Room and Two Betrayals can also be heard on this map.
 * Although the map takes place on Installation 00, the arms of the Ark are not visible. This is also the same for Epitaph, which takes place in the same structure.
 * If a player looks out of the "windows" with a scoped weapon, one can see what looks like a desert setting with a structure similar in appearance to the edges of a Halo Installation, only it appears to be made out of bricks and mortar.
 * If you look out the skylight windows, there is no evidence of the tower continuing. However, looking out of the side windows (and using the road-like metal objects outside as reference points) reveals that Citadel is closer to the ground than Epitaph is. The former would seem to imply that Citadel is at the top of the tower, but the latter proves that it is closer to the bottom.
 * This may have been a simple level design oversight. Using Pan Cam reveals that the developers completely removed the tower's exterior (such that in terms of the Citadel's 3D, the area is effectively a set of hallways floating in midair). They may not have noticed the resulting discrepancy.