The Age of the Wizard-Kings

During the Titan War, the gods empowered human worshippers to serve their cause, and in response, so did some of the titans. The techniques they taught mortals are still employed by adventurers today. When the war was won, some of these champions were able to seize scraps of knowledge and fragments technology from salvaged weapons of the gods and from plundered titan strongholds, even from the outer precincts of Heaven itself. 

One wily titan, eager for revenge against the traitorous gods, gave mortals the secret of the paths of Immortality--a means to make themselves near equal to the gods. When the gods shut the gates of the Overworld, barring mortals from Heaven, their former champions began seeking their own apotheosis. What wouldn't be shared, they reasoned, they would take.

Connecting with the pillars that supported the cosmos--the so-called Spheres of Matter, Energy, Thought, and Time--mortals began to walk the paths to Immortality. In the process, they discovered more secrets of the Cosmos's creators. They developed technology that allowed them to conquer the world and usher in an age of advancement and wonder with flying cities, automata, and sagacious, living libraries. It was also an age of excess and violence with strange monsters crawling from the subterranean laboratories and towering war machines wielding eldritch weapons to lay waste to cities. This time was known as the Age of High Magic or the Age of the Wizard-Kings.

The end of the Age came when internecine fighting had weakened the Wizard-Kings such that they could not defend against a succession of threats: the forces of Chaos launching sorties into the Cosmos, and irruptions of the Underworld caused by the Lich Lords, and continued subversion by the fiends from Hell. In the end, a coup by chromatic dragons toppled the most powerful surviving Wizard-Kings.

The remnants of their power remain, though. In the ruins of sky cities or in the depths of the dungeons they built adventurers still encounter they creations, technology and servitors. Perhaps somewhere the secrets of Immortality await the lucky delver?