The Nine Hells of Baator, is the home of the devils. It has a strict caste system with a very rigid chain of command. Unlike the demons of the Abyss, the devils were highly organized in their quest for power and status—scheming and plotting power plays, coups, and assassinations.
it is a plane shaped like a mountain turned on its head. The first layer is vast and the others get progressively smaller, though technically most are described as being infinitely large.