At the beginning of the 11th cent. a great wave of Seljuk Turks, led by Tughril Beg, conquered Khwarazm and Iran. They entered Baghdad in 1055; Tughril Beg was proclaimed sultan. Under his successor, Alp Arslan, the Seljuks conquered Georgia, Armenia, and much of Asia Minor, overran Syria, and defeated (1071) the Byzantine emperor Romanus IV at Manzikert, opening Byzantium (except for a small area around Constantinople) to Seljuk and Turkmen occupation. This irruption was a major factor in bringing about the Crusades, during which a three-part struggle among Christians, Seljuks, and Egyptian Mamluks developed. Alp Arslan's son, Malikshah (reigned 1072–92), ably administered and developed his huge empire; he was a protector of Omar Khayyam, who reformed the calendar at his behest. At the start of the 12th cent. the Seljuk empire began to fragment, and various parts achieved virtual independence. The attacks of the Khwarazm shah led to the final downfall of the empire in 1157.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.