Act III (Diablo III)
The third act of Diablo III takes place in Bastion's Keep. Belial is already captured in the Black Soulstone, and Azmodan wishes to claim it by sending his demonic army to attack Bastion's Keep from the Arreat Crater.
Bastion's Keep, originally built by Korsikk, is home to the Barbarians who remain after the events of Diablo II and the destruction of Harrogath and Mount Arreat. It stands guard against the now feral and violent tribes and monsters in the north from pouring into the southern lands.