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