Covenant citadel

The citadel is a Covenant base structure, and the Covenant equivalent of the UNSC Firebase in Halo Wars. It contains a Command Center, seven building sites, and four turret foundations.

When a new base has been claimed in standard Skirmish or multiplayer mode, the beginning base facility is called the Outpost. It includes a Command Center and three building sites, but no turret foundations. Outpost can be upgraded to a Keep, which includes a Command Center, five building sites and four turret foundations, and can be upgraded to a citadel.

Summary
The citadel is a basic command structure with defenses such as Wraiths, Ghosts, and Banshees, and can also be defended by base turrets. It also has a similar underground garage to the UNSC's Firebase. These provide field command facilities for invading or defending Covenant Armies. Much like its UNSC equivalent, it possesses seven expansion "sockets" for more structures for research, unit production and defense.

The available buildings that the citadel can provide are a Hall, Temple, Factory, Summit, Shield Generator, and a Warehouse. It is colored a deep purple, like most Covenant buildings, vehicles, and ships.

Expansions

 * Temple
 * Warehouse
 * Hall
 * Factory
 * Summit
 * Shield generator
 * Automated plasma turret

Units produced and available upgrades

 * Scarabs
 * Honor Guard Elites (Prophet of Regret only)
 * Cloaking Ability
 * Personal Shield
 * Brutes (Brute Army Commander only)
 * Jump Pack
 * Electric Shot
 * Suicide Grunts (Arbiter only)
 * Zeal
 * Defile

Trivia

 * Unlike the Firebase, the Citadel's buildings seem to be built by an orbital beam. The UNSC constructs their buildings underground.
 * In "Origins II", at the moment when the Covenant and humanity fight together against the Flood, one can see a Summit and a Citadel consumed by the Flood.

List of appearances

 * Halo Wars
 * Halo Legends
 * Origins
 * Halo: Blood Line
 * Halo Wars 2
 * Halo: Rise of Atriox