Baator
Baator: aka Inferno; the Halls of the Damned; the Fire Below. Few names evoke as many dramatic and terrifying images in the minds of mortals as The Nine Hells, and with good reason. Baator personifies the epitome of the Lawful Evil ethos as a place of punishment, oppression, and endless, soul-crushing conformity. It is the eternal destination for fascists, tyrants, despots, cruel overseers, malicious judges, unscrupulous barristers, and (most) politicians. Basically, anyone who dominates others through (legal) force or manipulates the law at the expense of others will probably find him-or-herself on a one way trip to the big H-E-Double hockey stick when they get their ticket punched.
Baator is made up of nine descending layers and does not resemble a certain Italian poet's vision of Hell at all. These nine descending layers form (conceptually, at least) an inverted cone, with the "largest" layer (Avernus) at the top and the "smallest "(Nessus) at the bottom (although theoretically each layer is infinite in size; go figure). Baator's layers each embody a unique vision of torment, misery, exile, and suffering and each is ruled by one of the dreaded Lords of Nine.
Avernus: Avernus, the first layer of Baator, serves as the proverbial "Gates of Hell" and is thus the layer most readily accessible from the outside. Avernus is an endless, rocky, blasted wasteland where lightning streaks across the blood-red sky and balls of molten fire periodically streak overhead before crashing into the dust-choked hellscape in a pyroclastic explosion. Lesser Devils herd petitioners (the souls of the dead) through the gates like cattle, prodding with spears and lashing with whips, pausing only to torment and humiliate the terrified, shrieking wretches according to their whim and fancy. Avernus also serves as the martial fields where the infernal legions muster and drill endlessly in preparation for the next battle in the eternal Blood War. Unlike the other layers, no one knows the identity or whereabouts of the archduke who serves as Lord of the First. In the absence of a traditional Lord, the Pit Fiend Bel oversees Avernus as both military governor and commander of its forces. Other notable inhabitants of Avernus include Tiamat, the evil mother goddess of all chromatic dragons and Kurtulmak, the spiteful, petty god of Kobolds.
Dis: Dis is both the name of the second layer of Avernus as well as its principle city. The two are used interchangeably, as the "City of Pain" sprawls endlessly across an iron wasteland to the point where it is difficult to determine exactly where one ends and the other begins. Far on the horizon, black mountain peaks thrust into the ash-green skies although no one can tell if the mountains surrounding the city are real or simply a mirage brought about by planar metaphysics. The iron walls of the city proper smoke with intense heat, causing painful burns to any exposed flesh. The air is filled with the acrid stench of hot iron and the screams of the miserable souls who are condemned to spend eternity building, tearing down, and rebuilding the city with their bare hands. The archduke Dispater, Lord of the Second, rules the City of Pain from an enormous citadel of iron and lead known as the Iron Tower. From here, he oversees the city's endless building projects while lording over his vassals with an iron fist.
Baator's most notable inhabitants are the baatezu (also known as Devils). The baatezu form the backbone of the infernal hierarchy that runs the Nine Hells. They serve as the rank and file soldiers in its armies as well as the clerks who maintain its labyrinthian bureaucracy. Baatezu are vicious, cruel, and power-hungry schemers who see their subordinates as mere pawns and their superiors as obstacles in their endless grabs for influence and authority. Unlike their chaotic counterparts (the loathed tanar'ri), the baatezu frame their actions within a twisted, nearly incomprehensible code of honor.
(more to come)