1911 Encyclopædia Britannica/Omar
OMAR (c. 581-644), in full ‘Omar ibn al-Khaṭṭab, the second of the Mahommedan caliphs (see Caliphate, A, §§ 1 and 2). Originally opposed to Mahomet, he became later one of the ablest advisers both of him and of the first caliph, Abu Bekr. His own reign (634-644) saw Islam's transformation from a religious sect to an imperial power. The chief events were the defeat of the Persians at Kadisiya (637) and the conquest of Syria and Palestine. The conquest of Egypt followed (see Egypt and Amr ibn el-Ass) and the final rout of the Persians at Nehāwend (641) brought Iran under Arab rule. Omar was assassinated by a Persian slave in 644, and though he lingered several days after the attack, he appointed no successor, but only a body of six Muhajirun who should select a new caliph. Omar was a wise and far-sighted ruler and rendered great service to Islam. He is said to have built the so-called “Mosque of Omar” (“the Dome of the Rock”) in Jerusalem, which contains the rock regarded by Mahommedans as the scene of Mahomet's ascent to heaven, and by the Jews as that of the proposed sacrifice of Isaac.