The Citadel
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Usage
Location:	Widow / Serpent Nebula / Milky Way Galaxy
Commissioned:	11000000000 BCE
Destroyed:	29 March 2253 CE
Role:	Large-scale mass relay Provide gateway for Reapers to enter galaxy. Serve as capital of a major galactic civilization(s).
Affiliation:	Democratic Brotherhood of the Zeioph Syndicate of the Arthenn Sovereign States of Farcrothu Legendary Commonwealth of the Aebomt Tleiqreobue Corporate Directorate Royal Union of Stryvet States Holy Collective of Aphras Heavenly Imperium of the Priwix Interstellar Dynasty of the Craddapt Galactic Federation of the Faff Alliance of Suns Commonwealth of Constellations The Great Growth Bastion Confederate Prothean Empire United Citadel Council of Species New United Galactic Front of Races Galactic Dominion
Battle(s):	Prothean War with the Reapers Fall of the Citadel Eden Prime War Battle of the Citadel Reaper War Citadel Siege Fall of the Citadel Operation: Stormwind Citadel Raid Post-Apocalyptic War First Battle of the Citadel Second Battle of the Citadel Third Battle of the Citadel Dominion Civil War Battle of the Citadel-Ark Battle of Eos
Technical specifications
Length:	44.7km
Diameter:	12.8km
Population:	13.2 million (not including Keepers)
Defenses:	Eight hundred GARDIAN defense batteries Wards that can close to create a protective caccoon Citadel Defense Fleet Citadel Security Citadel Police Department (under the Dominion) 30m of Carininium
Type:	City
Power:	Fifty centralized eezo cores.
Manufacturer:	Reapers

"The Citadel. It was said to be the largest, most majestic space station in existence. The capital of galactic government. The top of the food chain. Where all the wealthy cosmopolitans went to retire in luxury."

— Marcus Shepard's mental description of the Citadel.

The Citadel was a massive space station in the Widow system of the Serpent Nebula, and has been the capital of numerous alien civilizations throughout history, most recently as the capital to the Galactic Dominion. Built billions of years ago by the Reapers, the station has been used and inhabited by numerous civilizations, serving as their capital and their downfall. It served as the capital of the Citadel Council and, later, the Galactic Dominion, before its destruction on Eos. The remains of the station would later be found by the Andromeda Initiative just under 600 years later. Towards the end of the Second Heleus War, the remains of the Citadel were used by the Andromeda Initiative and Second Andromeda Initiative to build a memorial to Marcus L. Shepard, and after a few months, the settlement of New Citadel was established there to reinforce this.

Thought by every species that inhabits it to have been built by those that came before them, the Citadel was actually a massive mass relay from which the Reapers were able to enter the Milky Way galaxy when they begin their harvests. The Battle of the Citadel in 2183 CE put a stop to this however, forcing the Reapers to enter the galaxy more conventionally; because of this, the Citadel remained in the hands of the UGC until its capture by the Reapers in September 2186, where it was moved to Earth, and wouldn't be moved back to the Widow system until after 2200 CE.