AL-MAMUN, ABU ABBAS AB DALLAII (783-833). A caliph of the line of the Abbassides (q.v.), distinguished for his intellectual qualities. He was the son of Harun - al - Rashid. When Harun died, his brother Amin succeeded to the Caliphate; but his treatment of Al-Mamun led to war, and after five years of fighting Amin was slain and Al-Ma mun took his place (813). The early part of his reign was disturbed by revolts and heresies; but when affairs settled down lie fostered the culti vation of literature and science throughout his Empire, and Bagdad became the seat of academ ical instruction and the centre of intelligence. He had books translated from old and living languages:, founded astronomical observatories, determined the inclination of the ecliptic, had a degree of the meridian measured on the plain of Shinar, and constructed -astronomical tables of remarkable accuracy. He paid more respect
to science than to orthodoxy, and drew his serv apts from all countries and all creeds. In 827 he favored the heretical doctrines of the Mutazil ites, who asserted the free will of man and de nied the finality of the Koran. In the latter years of his reign lie was involved in war with the Greek Emperor Theophilus, and revolts broke out in various parts of his Empire. In 833, af ter quelling a disturbance in Egypt, he marched into Cilicia against the Greeks, but died sud denly near Tarsus, leaving his crown to Mutasim, a younger brother. Al-Mamun was the author of Inquiries into the Koran, a tract on AS'igns of Prophecy, and one on The Rhetoric of the Priests awl Panegyrists of the Caliphs. Consult Muir, The Caliphate (London, 1891).