The Great Cataclysm

The Great Cataclysm was the event which destroyed the old surface world of Nerilia, forcing most of the people underground for survival and leading to the rise of new creatures. The world was profoundly changed after the Great Cataclysm.

Events

The events that would lead to the Great Cataclysm were set in motion almost 70 years beforehand, when Emperor Cyrdin of the Cyrdian Empire learned about titans, the first creations of the gods, which held nearly godlike power themselves. Having already developed a method for creating artificial humans, he believed that he could replicate this power. He worked to create twelve titans of his own, which he planned to use as weapons to conquer the world.

Emperor Cyrdin miscalculated, however, and when the titans awoke, he lost control of them, and while a heroic group of insurgents managed to slay one, the rest escaped and grew into their full power. They quickly began to indiscriminately destroy anything they saw, their awesome power reshaping the very landscape as they wandered the planet. Most of civilization was eliminated during this time, and life as a whole was greatly reduced on the surface. Many survivors retreated into the Darklands underground.

Fortunately for what life remained on the surface, the titans' construction was flawed in more ways than one, and over time their bodies began to fail. They died, one by one, until at last the final titan fell and the Great Cataclysm ended, 75 years after it began.

Aftermath

The cataclysm wiped out nearly all civilization on the surface, forcing most of the few survivors to return to pre-societal hunting and gathering, but this was actually one of the least consequential of its effects. The titans were suffused with corrupted, volatile magic that they unleashed upon the world, and this had lingering, sometimes permanent, effects after their deaths. The very landscape, especially near a titan's corpse, became strange and fantastical, with permanent lakes of fire, land floating in the sky, and much more.

The magic also had a transformative effect on creatures, mutating them into new species with innate powers or simply new shapes. Halflings, many of whom survived on the surface, were transformed into gnomes, while the very few humans, elves, and dwarves who remained also turned into bizarre, often monstrous beings. Goblins and their kin, as well as orcs, were largely unaffected, having some innate resistance to the Cataclysm's magic, and rose to be some of the dominant humanoids. Many kinds of animals developed humanoid forms and intelligence, such as catfolk and ratfolk, and some extinct species, such as dinosaurs and the kongamato were brought back to life as they had been before. As a result, almost no non-magical species of animals that were alive during the Cataclysm still exist in the same form today.

The magic also warped the fabric of the universe around Nerilia, nearly completely disconnecting it from all other planes of existence. Only a tenuous connection to the River of Souls remains, and as a result, many dead souls fail to find their way to the afterlife, either being reborn in a newborn body, or else forming their own and becoming a demon, celestial, or other spiritual being. All the old gods that reside on other planes have no influence on Nerilia, and new gods have risen after the Calamity, many of whom are mortal creatures who accumulated enough power to ascend to divinity.

It took several hundred years before humanoid species had recovered enough to begin creating primitive new societies, some in the ruins of the old world, and others brand new.