It is said that the plane of Sheol first sprang into existence when the first human had his first impure thought. Now Sheol is an impossibly vast mountain floating in the Astral Plane. Its original seed still exists as the Axis Mali, the pinnacle of the mountain. Around it, the devil lords maintain their domains, each scheming to enlarge their own territory and striving to gain control of the pinnacle, which is said to grant ultimate power to any devil who can hold it for a year and a day. So far, none have succeeded.
Sheol constantly keeps expanding, as any devil who is slain on it turns reddish stone half-merged with the ground. Devil lords living close to the rim are expanding their territory by pushing the countless imps arising spontaneously on the mountain over it, as that kills them, expanding the base of the mountain with their deaths. But the territory becomes more desirable the closer it is to the pinnacle, and this highly contested land often rises significantly in elevation after major battles. But no matter how many millions of bodies of devils may fall around it, the Axis Mali always towers over its surroundings and illuminates the mountain with a blood-red light emanating from its top.
The domains of the devil lords cover the entire mountain, and it is rare that any given lord is not in a state of conflict with one or more of its neighbors. Even if there is no outright warfare, the lords constantly plot and scheme for supremacy, with cunning and intrigue often being as important as skill at battle. New devil lords usually have to stake out new territory close to the rim of Sheol where the competition is less fierce and new territory can be easily created. But sooner or later, they all try to expand towards the center. The most cunning, ruthless, and powerful survive and prosper, while the weak become yet more stone for the mountain.
But not everything on the mountain is focused on the eternal battles. All devils delight in having power over others, and thus communities have sprung up where the more powerful devils dominate the weaker ones. Lesser devils abuse the imps, Greater devils have numerous lesser devil slaves, and the devil lords rule by bending the greater devils to their will. Entire settlements and even cities exist all over Sheol where the devils can play their endless games of dominance. Only the cunning retain some measure of freedom from dominance, usually by ingratiating themselves with their superiors or by dominating their own rivals for power.
From time to time, brave overconfident humans dare to come to Sheol in search of power, knowledge, or rare items or services. They will not generally be attacked on sight when entering the towns of the devils, but they had better be both cunning and powerful to escape the many traps the devils will set in their attempts to dominate them in body and soul.
As devils spring up and grow from impure thoughts and sins, and the mountain consists of the bodies of dead devils, Sheol can be considered to literally consist of the accumulated sins of humanity and the other sapient races of Rothea. Some religions warn that one day Sheol will be so massive that it will one day break through the Astral Plane and drop into the Material Plane, causing the uncounted hordes of devils to run free on Rothea and subjugate all which is good and pure. In this future, only the gods will be able to protect the faithful. Until then, it is important that sins are fought wherever they are found.
List of Sheol Locations
Adventure Ideas
Designer's Notes & Resources
Perhaps I should dig through my old Planescape material so that I can make Sheol more like an evil version of Mount Celestia…
If you have any good ideas for specific locales or devil lords, add them in as non-canon material.