Black Chasm

Black Chasm has been a site of strife between the Skaven since Clan Pestilens returned from its long sojourn to Lustria. It was here that Pestilens’ ancestors made one of their earliest homes. Their ancient forebears carved out a series of strongholds within the limitless depths of the Black Chasm itself. The assassins of Clan Eshin claimed the abandoned strongholds for themselves, and refused to return control of them to Pestilens upon the clan’s return from the west. In modern times, Pestilens relies on its relationship with Clan Flem as it fights to regain its lost legacies, while Clan Eshin has been employing the Packmasters of Clan Moulder to better cement its position.

Source

 * Warhammer Fantasy RPG 2nd ED -- Children of the Horned Rat (pg. 54)