He is succeeded by his son al - Mahdi .
Caliph al - Mansur dies after a 21 - year reign , in which he has made Baghdad the residence of the Abbasid Caliphate .
al - Mansur is succeeded by al - Mansur 's son al - Mahdi .
Caliph al - Mansur dies after a 21 - year reign , in which he has made Baghdad the residence of the Abbasid Caliphate .