The Nine Hells were a concept proposed by some scholars regarding the structure within the Lower Realms, and was a somewhat controversial model of Devilish cosmology. Very few reliable sources from Somnum could be trusted for firsthand accounts, so instead relied on the notoriously unreliable word of lesser Fiends summoned to the Prime Material.
According to the model, The Nine Hells were built on strict laws and absolute control, only connected to each other by the River Styx. Each level of Hell served a function, breaking down the souls who entered and turning them into servants of the system. Power among fiends was maintained through fear, and escape was nearly impossible; generally, the only way to improve ones living conditions in hell was through power. For mortals, the more evil their soul and deeds were on the Prime Material, the lower they would be placed in the Hells, though even amongst scholars there was debate on which punishment was made for what type of criminal.
They Nine Hells were divided into a punishing hierarchy, with each level designed to enforce control and suffering:
Avernus, the first level, was a wasteland of constant warfare where infernal armies clashed under a burning sky.
Dis, the second level, was a vast city of iron, stretching endlessly with towers and fortresses and patrolled by devils to ensure order.
Minauros, the third level, was covered in endless rain and filth, swallowing anything that sank too deep into its swamps.
Phlegethos, the fourth level, was covered in lava flows and unbearable heat, where even the strongest devils struggled to survive.
Stygia, the fifth level, was a frozen wasteland, with vast glaciers that trapped both the living and the dead beneath their crushing weight.
Malbolge, the sixth level, was a landscape of crumbling rock that forced its inhabitants to navigate an unstable terrain where survival depended on constant vigilance.
Maladomini, the seventh level, was a land of ruined cities and failed ambitions, where structures collapsed as quickly as they were built.
Cania, the eighth level, was an expanse of ice and relentless storms, a place of treachery where the strong ruled through deception and brutality.
Nessus, the ninth level, was a land of deep chasms and endless darkness, where absolute power was concentrated in the hands of its ruler.