In the myth that Asmodeus created Baator (from the "Codex") it states that Asmodeus tortured souls in a far off section of the upper planes and that when their screams filled heaven the gods once again tried to remove Asmodeus from the upper planes, but by the Pact Primeval Asmodeus was allowed to torture the souls in heaven. Asmodeus offered the gods an alternative; give him the power to create his own plane of existence from which to torture the souls that broke heavenly law. The gods agreed and Asmodeus and his devils left and created the Nine Layers of Hell.