Atlantis was once the capital city of the seat of power for the Fae Athanteen. It was located on Earth, and was situated not far from the western shores of Italy, although it existed only in antiquity.
The city was a renown place of learning and philosophy, and the people there considered themselves the guardians of the world.
While the war has been underway for millennia by the time that Atlantis was destroyed, no real threat to the Universe was believed to exist until the Outsiders created or discovered an artifact that has come to be known as the Roark Skull. With this item, the Outsiders were able to bypass the Outer gates and conduct incursions directly into the Universe of Man.
The Old One Premiogothiq was able to open a rift to Atlantis and attempted to recapture the skull. He was killed and the City was driven into the sea beneath the mass of his falling corse, destroying it.