Atheia is the captial city of The Valley.
Before the Series
Atheia was the most prosperous of the valley. Rat Creatures attacked it and the royal family was almost completely wiped out. The city was rebuilt and taken over by the Vedu.
Atheia was mentioned in the beginning of the second book. Tom stated that he had combs from Atheia, and that hardly anything in the Valley compared to it.
Eyes of the Storm
Gran'ma Ben explained Atheia's importance during the Old Kingdom and how it fell.