Perhaps the best evidence to the origins of the Skaven lie in an ancient Tilean folktale entitiled the Doom of Kavzar. It tells of a city at the dawn of time, populated by humans above and Dwarves in the halls beneath it. Life was good for both the manlings and the Dwarves. It was decided that a great temple would be built to honor their gods. The work on the temple took generations, but finally only the great tower remained. Work slowed as the height increased, until it seemed to stop altogether.
A stranger appeared and offered the elders a proposition. He would finish their tower in a single night and all he wanted in return was to add his own dedication to the gods. His oofer was accepted and the stranger made good his promise. The manlings gathered before the temple just before midnight to marvel at the work that their grandfathers had begun. The stranger's dedication hung from the top of the tower, a great horned bell, but of him there was no sign.
The manlings rejoiced. At midnight the great bell tolled thirteen times. Great storm clouds began to gather and ominous lightning flashed across the sky. The manlings returned to their homes and in the morning the storm showed no sign of abetting. Black rain fell all that day and did so for weeks afterwards. Every night the great bell tolled thirteen times at midnight, and each day was worse than the last.
Fearful, the manlings went to the Dwarves for help. The Dwarves had no concern for a little rain and turned the humans away. Dark hailstones began to fall, followed by meteors of corrupt stone. Destruction was rained onto the humans, homes destroyed, babies born with strange mutations, the horrors were worse each day.
Once more the humans approached the Dwarves, who had troubles of their own. Their lower halls were flooded and vermin had consumed their food, just like the manlings' own supplies had been eaten. The humans were once more denied any help.
Men soon turned to the darker gods and even daemons for assistance, but none came. Rats became larger and bolder and hunted the manlings in their own city. The humans took up weapons and went once more to the Dwarves. They battered down the doors to the ancient halls to find only the gnawed bones of the Dwarves. All about them, glowing eyes watched. The tide of rats moved in for the kill. The manlings fought for their lives, but to no avail. The horde of vermin overwhelmed them, tearing at the flesh. The screams of the dying were drowned out by the chittering of the feasting rats.
Then, 1600 years before the time of Sigmar, the first true Skaven crept from beneath the empty city and became the undisputed masters of Skavenblight.