Reign of al-Mahdi (3 ene 775 año – 9 ene 785 año)
Descripción:
 During the reign of al-Mahdi, the administration of the Abbasid empire is expanded and specialized. Divisions known as Diwan are created, which are then headed by wazirs. 
Añadido al timeline:
fecha:
3 ene 775 año
9 ene 785 año
 ~ 10 years