The Green Lantern Citadel was a structure created by Power Ring energy and located in the hills of Northern California. The architecture of the building was designed by the Green Lantern Corp's resident architect John Stewart. The Citadel was used as the base of operations for the Green Lantern Corps at a time when the team was only seven members strong. Rather than patrolling a space sector as their predecessors once did, these Green Lantern's remained on the planet Earth, though their adventures often forced them to engage adversaries off the planet. When the Guardians of the Universe returned to the Milky Way Galaxy with plans to usher in a new Millennium, the Green Lantern Citadel became a de facto residence for several neophyte heroes who represented mankind's next evolutionary step. These heroes became colloquially known as the New Guardians.