The 20 years' caliphate of al-Ma'mum began as a stormy period in Middle Eastern history; after the comparatively peaceful reign of his father Harun al-Rashid, the caliphate was plunged into violent civil warfare in both Iraq and Arabia, involving the sons of al-Rashid, rivals for the supreme authority, and various other sectarian rebels and aspirants for power. Yet once peace was secured and the caliphate lands united once more, al-Ma'mum's reign...