Legend of the Abyss
The ancient and lost empire of the Elves from before the Tearing. According to the tales, Aelrretyn sought, and succeed, in destroying The Old Ones the gain their power. The power that the Elves of Aelrretyn used, however, caused the Tearing, and the intervention by Ásvaldr which ultimately led to the elven banishment to the surface and inability to use Arcane power without the blood of Humans.
Some relics from the Aelrretyn Empire exist and are highly sought after, some are found in the Unknown Depths for before the Tearing the Dwarfs where subject to the Aelrretyn Empire.