Astrae is the capital of the seraph empire.
Before the chimaera rebellion began, Astrae was a city of unrivaled beauty, with spires and architecture assisted by magic, but after the rebellion began it was destroyed and rebuilt. Still considered a beautiful place, it was still unable to claim it's former perfection after the war began. In the fist DOSAB book when the chimaera slaves of Astrae broke free, and burned down the seraphs library were they kept all their knowledge about magic. And over time the Seraphs had become so dependent on magic, that this was a great loss for them.