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 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 a Warehouse for providing resources. It is colored a deep purple, like most Covenant buildings, vehicles, and ships.

Expansions

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

Gameplay tips
As soon as you can move, make two Warehouses and one Temple. Wait for the Warehouses to create upon themselves and make a Hall whilst your Temple is building. Once your Temple is created, move Regret, the Arbiter or your Brute Chieftain somewhere. Buy the Citadel upgrade and wait for the Hall to create. Purchase the Blessed Warehouse upgrades for both Warehouses. Once the Hall is created, buy a shield generator. Citadels are incredibly weak without their shields. Once the shield generator is complete, create a Summit to supply yourself with aircraft and create Engineers to heal your forces. Create another Warehouse or a Factory with your last build site. Your base is almost complete. Create two turrets in front of your base. Once they are complete, make an upgrade depending on your enemy. With the Prophet of Regret upgrade it to Anti-Infantry to counter his Elite Honor Guards. With the Arbiter use Anti-Infantry to kill him when he is sent to your base. With the Brute Chieftain make it anti-vehicle since it is most likely he will send Locusts to your base. Any UNSC enemies create Anti-vehicle to destroy the Scorpions and the Hornets or Hawks. From there you are ready to build your army to crush the enemy and win your match. Don't forget to defend your Shield Generator and the Main Building. Also, another strategy is to build all Shield Generators on your base, this will keep it safe until a massive army arrives. Another tip in Skirmish is to have a second base (you will most likely need to defeat an enemy base for this to be possible). Make the base closest to the enemy to have one upgraded resource building, and the rest of the expansions to be unit creators (have a Shield Generator or two built if playing as Covenant). Then have the other base all upgraded resource generators (and a Shield Generator if Covenant). If implementing this strategy as the UNSC, always have your turrets built with the Gauss upgrade (anti-vehicle), and the Fuel Rod upgrade if Covenant. Try to also have turrets built with the Large Turret upgrade for all your turrets if possible and at least two tanks guarding each base.

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

 * The back of the Covenant bases bears a resemblance to the Elite Commando armor permutation.
 * 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, you can see a Summit and a Citadel consumed by the Flood.

List of appearances

 * Halo Wars
 * Halo: Blood Line
 * Halo Legends
 * Origins