In Dark Souls, the city destroyed by the Abyss in the DLC’s past timeline is Oolacile.
Oolacile is the setting of the Artorias of the Abyss expansion. The player is drawn into the past by Manus and explores the remnants of a civilization consumed by the Abyss. The area includes Oolacile Sanctuary, the Royal Wood, Oolacile Township, and the Chasm of the Abyss.
The story presents Oolacile as a society that awakened and disturbed an ancient darkness. Its ruined architecture and hostile inhabitants show how the Abyss transformed the city and its people. The expansion also connects Oolacile’s catastrophe with Artorias, Manus, Princess Dusk, and the intervention of the player character.
Oolacile is easy to confuse with New Londo because both are linked to the Abyss. New Londo is a separate Lordran region destroyed after its inhabitants became Darkwraiths. Oolacile belongs to the DLC’s historical setting, while New Londo is part of the main game’s present-day journey.