Ratmen, popularily known as "Skaven" once ascended from the dark depths of the Fell Craag, a giant chasm previously thought to be unhabited. They started out as raiders along the roads of the Lordship of Lordren, and quickly adapted to be deft assassins and warriors during wartime.
During the Great Goblin War (45 AD - 50 AD), the allied forces of Gutenbad allied themselves with the Skaven. The Skaven clansmen hold the glory to a wide variety of assassinations performed on the enemies leader, including the Goblins Elder Seer, Formabo the Long-Eared.
After the war, most Skaven learned to co-exist better with the other inhabitants of Lordren, and became a common sight in most Trader-Cities.