Th capital of Bael-Turath is Asmodeus. No, not the devil-turned-god, but a hellish metropolis built upon his corpse, chained to what remains of the Nine Hells (an iron spehere).
The city is ruled by a tiefling who claims to be directly descended from Asmodeus himself. Laws are complex and strictly enforced. The denizens are divided into castes, with arcanists and nobility on top and slaves firmly entrenched at the bottom. Devils are commonplace, and souls are a currency, fuel supply, and crafting material.
The players have not been here, and for their sake they might never have a reason to go here. Hopefully--for me at least--they find one. :-)