Burning Hells

The Burning Hells, otherwise referred to as the Netherworld, or simply Hell, are the birthplace of demonkind and the opposing realm of the High Heavens. All demons have their point of origin here and if struck down, will reform in time, namely from the Black Abyss.

Lore
A network of subterranean caverns runs throughout Hell. Molten rivers flow throughout the realm, numerous mesas feature, and Hell features "vast planes" across which Siege Beasts rampage. Hell is cloaked in perpetual twilight, and carries the stench of sulfur. To mortals, walking into Hell is like walking into a blast furnace. Much of Hell has a high temperature, but not so high that humans cannot withstand it (albeit with discomfort). Hell is said to have "corrosive influence," and this can be seen in the ruins that dot the realm.

The Hells are divided into seven realms, each corresponding to one of the Seven Evils, and can geographically be distinguished between upper and lower regions. Every level of Hell exists in a void, with 200 feet separating each level from each other. No walls mark the edge of Hell, and flying creatures frequently travel between Hell's levels. The seven realms are located in the center of Hell, while the outer reaches of Hell are controlled by enormous demons called the Mallet Lords. Hell is rife with war, both external and internal.

The souls of the most ruthless, hate-filled and aggressive soldiers of mortal wars often come to reside in Hell, residing in fires of eternal punishment. These souls range from mortals to even Devils, Fallen Angels, Angels, and Gods.

At times, over the centuries, Hell and Sanctuary (Earth or Draconic Deus) touch each other in a manner that allows the summoning of demons into the mortal realm to be easier than it might otherwise be.

History
Like all of Creation, Hell was created in the final battle between Anu and Tathamet, the corpse of the latter giving rise to the realm and demons erupting from it as maggots would from a corpse. Unlike Heaven, which has clearly defined borders, the realms of Hell were constantly shifting, the realms of influence varying under the seven Great Evils. Like Heaven though, Hell was indeed a physical location within the universe, though on the occasion that demonic incursions were launched against Sanctuary en masse, demons erupting from the ground is a common M.O.

It was due to Sanctuary's existence that Hell fell into internal conflict. Even after the Sin War, the Prime Evils believed that humans could be converted to their creed, while the Lesser Evils saw their focus on humanity as an unwanted deviation from the Eternal Conflict. The result was a civil war that resulted in the Dark Exile, though in the aftermath, Azmodan and Belial broke their alliance and fought one another.

Lucifer's Revolution
Prior to the Great War of the Three Factions, the Seven Evils had captured and enslaved Lucifer and his fellow Angels who fell from the grace of Heaven. Dragged down to the Burning Hells, the Angels were tortured and mutilated by them, forced in hard labor serving their masters as slaves in building their dark army. In the process they began experimenting on these new Angels, changing and manipulating their essence in an effort to make them more demonic. Thus the first Devils born of Lucifer, Asmodeus, Leviathan and Beelzebub were born.

After countless years of slavery, Lucifer and three other powerful Devils; Asmodeus, Leviathan, and Beelzebub; gathered much of their enslaved kind and rebelled against their demonic masters in a revolution that culminated in them taking a small portion of the Burning Hells and severing it from the main body to create their own realm: The Underworld. To accomplish this, Lucifer acquired a shard of the Worldstone and used its power to cut the realm away from Hell, like a knife through butter. The shard was then utilized to form the Underworld in the Devils' image, making it their new home. Lucifer then erected a barrier to separate the Underworld from Hell to ensure the demons do not gain access to their realm.

Knowledge of the Burning Hells and of the Seven Evils were known only to the Four Great Satans, along with the descendants of the Underworld's original rulers. They kept the true story of their kind away from the public to not spread fear amongst the populace. But they did prepare for Hell's inevitable return and the war that would come.