Bhall fell through the plane and brought their city Braduk with her. (I think?)
Then the Ember orcs built the city Braduk the Burning around the burning crater or something.
Men mimicked the gods during the Age of Magic. There was no good magic in that age, all sorcery was dark and corrupt so the most fierce battles were between the armies of the wizards and those of the holy. Eventually the one empire of men was split by this war into 10 countries.
One of those countries, the Bannor, was made up of the most pure. Fire was the weapon of the holy and Bhall was the greatest enemy of the corrupt. The Bannor venerated Bhall, they burnt evil cities to the ground and it is said that the holy could walk through fire without being burnt in those days.
Agares realized that it was only a matter of time until the Holy won their war. The countries that venerated evil gods were growing weaker. The greatest students of Kylorin were falling, Laroth and Gastrius were dead, Perpentach was locked within the Tower of Eyes (which held his body, but his mind wandered through creation and farther reaches).
So Agares began whispering to Bhall, playing to her pride. She was the greatest angel, enemies fled before her armies. The compact allowed a god to act only accoridng to the faith of her followers, and that gave Bhall the greatest power in creation. The evil god she was responsible for opposing, Mulcarn, was the least of the gods. The few people that followed him were relegated to the wastes, inconsequential and without power.
But Bhall's fall from heaven changed everything. The world caught fire, meteors pummeled creation, fields burned. But that didn't compare to what happened to the Bannor. Most strongly tied to Bhall they were transformed into cruel mockeries of mankind. Strong and savage, bones tore through their skin and their holy crusades became a bloodlust they could not control.
The greatest temple of Bhall was in the Bannor capital of Braduk. And Bhalls fall was literal. She fell through her vault, through the sky, through creation, through the world and into hell. She struck the world at Braduk and although most of the people were killed instantly some were dragged into hell with her.
Deep in hell and abandoned by their goddess no one expected these lost Bannor to survive. And they wouldn't have if Junil hadn't sent Sabathiel to guide them. It was a long difficult path through generations of the Bannor bent on survival. Their survival through the physical threats was the stuff of legend. But the real threats of hell are more insidious. Any spiritual weakness, any temptation was exploited and those that couldn't remain pure were a risk to the survival of everyone. Strict rules were developed, it was only a fanatical devotion to those rules (both in the physical and the spiritual) that allowed them to survive. A devotion that exists to this day.