Abyss

The Infinite Layers of the Abyss was the birth place of the demons, a chaotic evil universe unto itself with uncountable layers of infinite variety connected haphazardly. The Abyss's place in the cosmology of the Forgotten Realms shifted over time, but the nature of the plane remained fairly constant: a violent, malevolent place where the strong survived on the backs of the weak, the weak conspired to overthrow the strong, alliances only lasted while convenient, and the landscape itself tortured the mind and body of all who dared to pass.

Cosmology

In the Great Wheel Cosmology model, the Abyss was an Outer plane on the Great Wheel connected to the Astral plane, Pandemonium, Carceri, and the Outlands. Some estimated that the Abyss had 666 layers, while the Fraternity of Order claimed to have catalogued 679 layers. It was possible that the number of layers was infinite, but no one could be certain. The first layer, named Pazunia after the demon Lord Pazuzu, was described as a barren, dusty place baking under a red sun, broken only by great iron fortresses, huge holes in the ground, and the river Styx. Some branches of the Styx flowed down the holes (which were conduits to the various layers) and some of these holes supplied water to the Styx in reverse waterfalls.
When the Great Wheel model was replaced by the World Tree cosmology model, the river Styx was renamed the River of Blood and it flowed through all the fiendish planes (except for the Supreme Throne and the Demonweb Pits) originating in the Abyss, passing through the Blood Rift—an unusual plane that connected the Abyss with the Nine Hells—bringing the demons even closer to their arch-enemies the devils, resulting in the Blood War. Cosmologists found evidence of portals between the Abyss and the Barrens of Doom and Despair, Clangor, the Demonweb Pits, and Hammergrim, with intermittent portals to Deep Caverns and Fated Depths. The Astral plane connected all of the fiendish planes to the Prime Material Plane, but not directly to each other.
After the Spellplague, Asmodeus consumed the essence of the fallen Azuth and ended the Blood War by casting the Abyss to the furthest depths of the Elemental Chaos. The World Axis cosmology described the ruined Abyss as a domain with ever-changing features and realms, where the demons waged futile wars over meaningless empires. Once again the river Styx flowed through the Nine Hells and the Abyss, but then emptied its pollution into the Astral Sea. Other than the Styx or braving the Elemental Chaos, the only known passages to the Abyss were found in the Demonweb Pits, the Dismal Caverns, and Nishrek.

Layers

The number of layers in the Abyss was unknown and perhaps unknowable, but this article attempts to list them regardless of which cosmology model was in favor at the time of discovery. Each layer had its own characteristics, which were as varied as the demons themselves. All types of terrain, atmosphere, weather, gravity, and material composition were represented in the myriad layers. Some examples were:
Air-dominant—zero gravity, no matter except air Ash—blowing dunes of ashes Battleground—Blood War or other City—warrens and slums to citadels and palaces, teeming with demons Earth-dominant—solid rock tunneled by the inhabitants Fire-dominant—everburning flames with salamanders, etc. Delusion—appears to be Normal but the flowers are poisonous or the trees attack Desert—endless tracts of black, white, or red sand with no water Glacier—infinite black, white, or orange ice with few rocky peaks breaking the surface Hellscape—a burning mix of magma, rock, and belching brimstone Maelstrom—swirling, bubbling chaos like Limbo Mountainous—rocky crags, precipitous cliffs, soaring peaks Negative-dominant—major or minor Normal—similar to a Prime plane with various flora and fauna Ocean—a trackless ocean, with a surface Salt—crystalline badlands or desert Sea—of acid, blood, garbage, insects, oil, or worms, etc. Swamp—noisome bog inhabited by predators Undead—specters, spooks, and ghosts Volcanic—lava flows, earthquakes, volcanoes, and smoke Water-dominant—nightmarish creatures in the murk

Inhabitants

There were myriad types of demons, too numerous to catalog here. Non-demonic life could be found in the Abyss but was most likely imported from other planes.

Afterlife

Beliefs about the journey of souls to the afterlife changed with the shifting cosmologies and the crystal sphere in which one resided. In some worlds, chaotic evil souls would travel directly to the Abyss and become manes, the lowest form of sub-demon. Manes were treated as slaves, cannon fodder, and food by the demon lords. For mortals of Realmspace, however, all souls would first go to the Fugue Plane and await transport to their final resting place. Greedy demon lords would open a portal to the Fugue Plane and conduct raids to steal souls and bring them back to the Abyss to become manes. After the Spellplague, Shar reshaped the Plane of Shadow and folded in what death energy did not get absorbed into the Elemental Chaos and created the Shadowfell. After that, souls on their way to the afterlife started their journey in the Shadowfell and most made it to the Fugue Plane to await judgment, but a few remained behind or were lost.

Owner/Ruler

Tharizdun