The Abbasid caliph Mamun (813-33), the second of Harun al-Rashid's three sons, ultimately overcame his brothers to succeed his father as caliph. The son of a concubine from northern Afghanistan, he initially served as governor of the immensely rich and powerful province of Khurasan in northeastern Iran. After four years of bitter civil war, Mamun's army triumphed over that of his older brother Amin. In winning, however, Mamun alienated the population of Iraq and the defeated army, whose support he and his successors desperately needed. He died in 833 but never resolved the problems of holding together and religiously legitimizing his rule over an empire that stretched from Egypt to Central Asia.
Mamun was the most intellectual of the Abbasid caliphs, espousing a rationalist view of Islam. He transformed the caliphal library, which his father had founded in Baghdad into a virtual university. This remarkable institution, which was modeled on the Sasanian academy at Jundishapur in southwestern Iran, maintained a staff of translators, as well as copyists and bookbinders. He sent a delegation of scholars to purchase philosophical and scientific manuscripts in Constantinople, the Byzantine capital. Mamun also had books translated into Arabic from Syriac and Greek, Persian and Sanskrit, making the knowledge of past and foreign civilizations available to Muslim scholars.