The witches are a guild that accepts only women. They reside in the tower called the Witches' Keep, located next to the torturers' Matachin Tower in the Old Yard of the Citadel complex in the city of Nessus. Their patron saint is Mag.
According to legend, the guild was formed after the autarch Ymar the Almost Just ordered that there should be no more women in the Torturers' Guild, since the women were very cruel and often exceeded the punishments he had decreed. The basis of this legend is probably Prefect Prisca, a sadistic female leader of the jailers during the Age of the Monarch.