went (about 641). It is perhaps owing to these immigrants that the Arabic language so rapidly gained ground among the Jews of Babylonia, although a greater portion of the population of Iraq were of Arab descent. The capture by Ali of Firuz Shabur, where 90,000 Jews are said to have dwelt, is mentioned by the Jewish chroniclers. Mar Isaac, chief of the Academy of Sura, paid homage to the caliph, and received privileges from him. The proximity of the court lent to the Jews of Babylonia a species of central position, as compared with the whole caliphate; so that Babylonia still continued to be the focus of Jewish life. The time-honored institutions of the exilarchate and the gaonate—the heads of the academies attained great influence—constituted a kind of higher authority, voluntarily recognized by the whole Jewish diaspora. But unfortunately exilarchs and geonim only too soon began to rival each other. A certain Mar Yanḳa, closely allied to the exilarch, persecuted the rabbis of Pumbedita so bitterly that several of them were compelled to flee to Sura, not to return until after their persecutor's death (about 730). "The exilarchate was for sale in the Arab period" (Ibn Daud); and centuries later, Sherira boasts that he was not descended from Bostanai. In Arabic legend, the resh galuta (ras al-galut) remained a highly important personage; one of them could see spirits; another is said to have been put to death under the last Umayyad caliph, Merwan ibn Mohammed (745–750). The Umayyad caliph, Umar II. (717–720), persecuted the Jews. He issued orders to his governors: "Tear down no church, synagogue, or fire-temple; but permit no new ones to be built". Isaac Iskawi II (about 800) received from Harun al-Rashid (786–809) confirmation of the right to carry a seal of office. At the court of the mighty Harun appeared an embassy from the emperor Charlemagne, in which a Jew, Isaac, took part. Charles (possibly Charles the Bald) is said to have asked the "king of Babel" to send him a man of royal lineage; and in response the calif dispatched Rabbi Machir to him; this was the first step toward establishing communication between the Jews of Babylonia and European communities. Although it is said that the law requiring Jews to wear a yellow badge upon their clothing originated with Harun, and although the laws of Islam were stringently enforced by him to the detriment of