Citadel

Citadel is a Halo 3 map that was released on September 22, 2009, with Halo 3: ODST, as a part of the Mythic II Map Pack. 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 on the ground floor of the shield towers from the Halo 3 campaign level, The Covenant. 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

 * A good start to secure the rocket launcher is to grab a BR or carbine and destroy the power cores on the other side. This weakens the enemies for easy headshots and allows your team's possession of the rockets.
 * There are many angled walls in this map, making grenades an ideal choice when going into a potentially hostile area.
 * 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.
 * When playing in free for all, it is vital you control a power weapon as soon as possible.
 * The small size of this map makes players often pass up the sniper rifle. If you are good at no-scoping, then the sniper can be helpful when looking at the rocket platform.
 * It is possible to jump to the other team's 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
The following achievements can be unlocked on Citadel across the Xbox 360 and Halo: The Master Chief Collection editions of Halo 3.

Easter eggs

 * 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.

Trivia

 * 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.
 * 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, only it appears to be made out of bricks and mortar.
 * It is possible, in Forge, to go under the glass floor in the middle of the map. You can even go to the bottom of the hole and place objects.
 * 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.
 * Citadel seems to be set at the top of the tower, if the player looks upward while standing on the elevated area in the center of the map, the player will see sky. However, when on Epitaph and looking upward, Citadel cannot be seen. This disproves the idea that Citadel is at the top of the tower.