The Citadel of Oa

The Citadel of Oa is located on the planet Oa, and is the headquarters and meeting hall of the Guardians of the Universe. Millennia ago, the Guardians used the citadel laboratories to create a robotic army of soldiers to safeguard the universe. These beings became known as the Manhunters, but they later rebelled and left Oa permanently, taking up new refuge on the planet known as Biot. Centuries later, the Guardians established a new peacekeeping task force known as the Green Lantern Corps. The citadel became a training center and proving ground for the Corps. Members of the Green Lantern Honor Guard such as Kilowog and Tomar-Re recruited fresh warriors to train and serve in the Corps. The citadel houses the Central Power Battery of Oa - a resevoir of energy which embodies raw willpower. It is also where the mysterious Book of Oa is kept, specifically in one of the Guardian's main stronghold rooms known as the Hall of Great Service. The Guardians select chosen Green Lanterns to serve as Keepers of the book. In the first wave of the Green Lantern Corps, the Keeper of the Book of Oa was Tomar-Re. With the rebirth of the Corps, the position was handed to the ever-stern Slyggian, Salaak. The Oan Citadel also houses hundreds upon hundreds of Sciencells - spherical containment capsules where the worst intergalactic villains of the universe are imprisoned.