Atreia (Aion)  

Aion Wikibase™ Dictionary

Millenia ago, in a great cataclysm, Atreia was sundered, split into 2 worlds: Elysea below, always in light, and, Asmodae, above, forever in darkness. Between the 2 worlds stands The Abyss, the eternal battleground between the two halves of what was once one race.