Their father , Caliph Harun al-Rashid , had named Name_conferral al-Amin as the first successor , but had also named Name_conferral al-Ma'mun as the second , with Khurasan granted Giving to him as an appanage .

Commanded Control by the Abbasid heir-apparent , the future Harun al-Rashid , the Abbasid army reached Arriving as far as Chrysopolis , across the Bosporus from the Byzantine capital , Constantinople , while secondary forces Causation raided Attack western Asia Minor and defeated Conquering the Byzantine forces Causation there .