The Return of Darkness

A thousand years ago, the stories tell, what was then the Raurin Empire was beset by a terrible evil. Darkness reigned over the land, fire fell from the sky, and the people were filled with despair. It was then that the archmage Martek appeared, plunging into a terrible battle with the Great Darkness. Sheets of flame washed over the sky and the ground shook as horrifying roars filled the air. The sand around the city of Medinat Muskawoon burned with magical flame, and when it died down it had formed a huge, deep lake of glass which became known as the Skysea. When the conflict ended, Martek was victorious and the Great Darkness was gone. 
However, Martek made a prophecy: the Great Darkness was bound for a thousand years, but it would return. In a thousand years the evil would once again stretch its shadow over the land. At that time a group of heroes would appear, and they would discover Martek's Sphere of Power. When his Sphere of Power was used, the Great Darkness would finally be defeated and the Raurin people would be free of it forever.
The Raurin Empire fell only a few short years later, brought low by the fear and hubris of its final Pharaoh, Amun-Re. As the people scattered they bore the story with them, although many of the details have been lost in the intervening time. The myths of the prophecy all hold in common that the evil will return a thousand years after Martek vanquished it, and that a group of heroes would arise to unearth his Sphere of Power and defeat it forever.
Although the myth is no longer widely known beyond the Desert of Desolation, it is kept alive in the oral histories of the desert dwelling tribes. They are the last survivors of the people who originally suffered under the Great Darkness, and they have sworn never to forget those days, and to prepare for the heroes' arrival.