The Nine Hells

The Nine Hells of Baator, sometimes Hell or Hells, also known as "Baator" in Infernal, was the home of the devils. It was a plane of sinister evil and institutional cruelty organized in a strict caste system with a very rigid chain of command - many say it was where the term "lawful evil" originated from. Unlike the chaotic daemons of The Fade, the devils were highly organized in their quest for power and status—scheming and plotting power plays, coups, and assassinations. Each of the nine Hells had its own physical laws or properties of matter, but all were inhospitable or deadly to outsiders.

Geography

The river Styx flowed through all the fiendish planes originating in The Fade, passing through the Blood Rift—an unusual plane that connected The Fade with the Nine Hells—bringing the devils even closer to their arch-enemies the daemons, resulting in The Blood War.
Each of the nine Hells was unique and usually mirrored the malevolent characteristics of its ruler, or perhaps the archdevils were shaped by the domains they schemed to control, no one can be certain. What follows are descriptions of the nine Hells reported by various cosmologists working under different cosmological models, gathered, collated, and summarized:

1st: Avernus

The first circle of Hell was also the "topmost" because Astral travelers would emerge from blood pools on this layer and reaching the next circle required descending to the lower depths to breach a barrier to Dis. By all accounts Avernus was a desolate wasteland with rocky terrain, sparse, twisted vegetation, concealed snake pits, caves and warrens, volcanoes, and rivers of magma. The sky was starless, full of choking smoke, and glowed a dark red due to balls of flammable gas that floated about or streaked across the atmosphere, randomly exploding as a fireball. During The Blood War, Avernus echoed with the marching of legions of devil troops preparing for the next campaign against the demons of The Fade, the ground was littered with the detritus of countless battles and blood trickled out of the ground in vein-like streams eventually flowing into the river Styx.

2nd: Dis

The second circle of Hell, when described as its own layer, was a flat barren plane containing little more than black, stagnant rivers, stretching for thousands of miles until it reached some rolling hills. The sky was a cloudy dull green shot through with lightning. In the center of this plane rose the Iron City of Dis, several miles in height and hundreds of miles wide. The foul rivers radiated from a moat big enough to be called a lake surrounding the Iron City. The walls of the buildings and the stones of the streets glowed the dull red of hot iron; more than brief skin contact resulted in severe burns. Prisoners of war, tormented underlings, criminals, and kidnap victims were kept in underground dungeons where their wails of woe could be heard filtering up through small vents in the iron walls. Above it all rose the Iron Tower where Dispater sat and schemed, untouchable.

3rd: Minauros

Minauros as a layer was described as an endless bog of vile pollution, decaying bodies, and rotting marsh, repeatedly drenched by rain, sleet, and hail storms. The soggy, bone-strewn, disease-ridden swampland made movement very difficult and was only broken occasionally by serpentine ridges of volcanic rock. Nameless creatures even the devils feared inhabited the swamp. Minauros as a realm was depicted as a broad but low-vaulted cavern connected to Dis. An oily water percolated through the roof of the cave and rained down upon swamps, deserts of mud and oozing black soil, pockmarked by bubbling fumaroles and mud geysers.

4th: Phlegethos

The fourth circle was the Hell that most resembled the stereotype of a fiery world of eternal damnation, filled with active volcanoes, rivers of liquid fire, molten rock, ash hills, smoking pits, unbearable heat, all wracked by tremors and earthquakes. Even the air seemed aflame and thus Phlegethos was considered to be fire-dominant. Phlegethos was a cavern several miles below Minauros, where burning lava poured out of fissures in the ceiling. The city of Abriymoch was the seat of power in this realm, built of hardened magma, obsidian, and crystal in the caldera of an extinct volcano which provided visitors some protection from the elemental environment found throughout the rest of the plane.

5th: Stygia

The complete opposite of Phlegethos, Stygia was a bottomless ocean covered by an ice sheet up to 3 miles (4.8 kilometers) thick, condoned with huge icebergs. The river Styx cut across the ice forming a channel. A few floating islands were the only non-frozen ground in Stygia, their peaks wreathed in lightning arcing from the coal-black sky. Where lightning struck, a strange phenomenon called "cold fire" erupted: white flames of extreme cold that "burned" for a short time and then disappeared without a trace.

6th: Malbolge

Malbolge was a gargantuan tumble of angular black stone blocks, each block ranging in size from a small city to a large metropolis, that formed a pile hundreds of miles thick. The randomly tilted and ill-fitting blocks were honeycombed with angular passages and caverns causing non-flying travelers to frequently need mountaineering skills and risk avalanches. Stinking clouds of vapor rose up from the depths and lit the sky with the color of blood, causing cosmologists to speculate that the blocks of Malbolge may have rested on an infinite sea of lava. Corroborating reports have been heard of flammable materials left on the ground spontaneously combusting. Most habitations in Malbolge were copper-clad fortresses built from black stone.

7th: Maladomini

The seventh circle of Hell is described it as a colossal maze of passages each several miles across that eventually led to Cania, Malbolge, and Nessus. It was filled with ruins of old cities, stagnant rivers, exhausted and abandoned quarries and strip mines, stone aqueducts and lava canals, decaying fortresses, swarms of biting flies, and black pools of ichor that erupted from the ground. The Lord of the Seventh was never satisfied with the construction of his capitol and repeatedly built and abandoned city after city. The largest and most beautiful was Malagard, a sprawling metropolis with myriad black towers linked by a tangled web of bridges and walkways. Malagard was rumored to contain a million rooms and to cap an equally complex dungeon labyrinth.

8th: Cania

Cania was a bitterly cold-dominant realm of solid ice mountains, titanic, unnaturally fast-moving glaciers, and nearly continuous snowfall that made Stygia seem balmy by comparison. Unprotected travelers were exposed to temperatures of −51 ℃ but on the positive side there were few creatures that hunted in the icy wastes. Earlier lore described the great citadel Mephistar as being constructed of iron but later reports say the Lord of the Eighth's palace was made of ice. All accounts seemed to agree the tower had a heated, luxurious interior and sat atop a gargantuan glacier called Nargus whose speed and movement were under the control of Mephistopheles himself.

9th: Nessus

The ninth and deepest Hell was a land of extremes: regions cold as Cania, volcanoes like Phlegethos, a lake of ice, a flaming forest, sheer cliffs, firewinds and a citadel even larger than any other. Our view of this layer did not contradict this description of Nessus but focused more on the blasted and torn landscape out of which rose Malsheem, the Citadel of Hell. It was said that Malsheem could hold millions of devils within its mountainous edifice, from the lowest warrens deep in the trench to the soaring spires miles above the tortured plane. All reports agree that a progression of rifts, pits, and chasms lead down and down, forming a vertical maze hundreds of miles deep that contained great cities, fiendish armies, and the mighty fortress of Hell's Overlord Asmodeus.