 Complete the following phrase:  Jafars prominence increased during the reign of al-Mamuns successor al-Mutasim , who employed him in several of the campaigns of his caliphate. In 837 he and Itakh were sent by the caliph to reinforce al-Afshin against the rebel Babak Khorramdin in Adharbayjan, and he played a leading role in the effort to take Babaks stronghold of al-Badhdh. In the following year he was placed in command of the caliphs left wing during the 