'Ali b. Muhammad was the leader of the black slaves who had been imported into southern Iraq to clear and desalinate vast tracts of agricultural land. Under his charismatic leadership the rebels held out in the marshes of southern Iraq for thirteen years, until their ultimate defeat in 271 by the forces of the Abbasid caliph al-Mu'tamid. He founded a fortified capital in the marshes, which was called al-Madinat al-Mukhtara, "the chosen city". On his coins he is known by the title of al-Mahdi.