Twilight Citadel was a Feat of Templar Engineering 200 years in the making. A hollowed out and terraformed Asteroid designed to hold up to a million Templars safe. It was meant to be mobile, Equipped with a Class 6 Hyperdrive and more than 4 times the standard number of Null quantum field generators needed for something its size due to its unusual shape and composition.
Work on the project began in 120 BBY and while the Terraforming was finished within a few decades the Sublight and Hyperdrive engines needed to be perfect, or as close to as possible and took one hundred and seventy years to perfect, being completed only at the onset of the Sith-Imperial War.
Halfway through construction the basis of the facility shifted from being a praxeum ship, to a mining facility.