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 7 expansion "sockets" for more structures for research, unit production and defense. The available buildings that the Citadel can provide would be a Hall, Temple, Factory, Summit, Shield Generator, and of course a Warehouse for providing resources. It is colored a deep purple, like most Covenant buildings, vehicles, and ships.