With the division of the Roman Empire into two halves the Greco-Judean colonies on the Black Sea were naturally drawn into the sphere of influence of the eastern part, the Empire of Byzantium, the capital of which, Constantinople, was situated on the opposite coast of the Black Sea. Commercial relations brought the Taurian colony into ever closer contact with the metropolis of Byzantium, and the Jews vied with the Greeks in the promotion of trade. The persecutions of the militant Church of Byzantium under the Emperors Theodosius II., Zeno, and Justinian, during the fifth and sixth centuries, drove the Jews from the ancient provinces of the Empire into the Taurian colonies. In the eighth century the Jewish population of these colonies was so numerous that the Byzantine chronicler Theophanes places the Jews in the forefront of the various groups of the population. "In Phanagoria and the neighboring region," says Theophanes, "the Jews who live there are surrounded by many other tribes."
These colonies were frequently visited by Christian missionaries, who endeavored to convert the native population to their faith, and incidentally also to win over the Jews. The Patriarchs of Constantinople were then hopeful of drawing the people of the Old Testament into the fold of the New. The Patriarch Photius, of the ninth century, writes thus to the Bishop of Bosporus (Kerch): "Wert thou also to capture the Judeans there, securing their obedience unto Christ, I should welcome with my whole soul the fruits of such beautiful hopes." The "Judeans," however, not only did not take the bait of the missionaries, but even managed to spoil their propaganda among the pagans. The most illustrious of all Byzantine missionaries, Cyril and Methodius, had frequent occasion to quarrel with "the Judeans, who blaspheme the Christian faith," and the boastful ecclesiastic legend asserts that the holy brothers "by prayer and eloquence defeated the Judeans [in disputes] and put them to shame" (about 860).
The struggle between the Christian missionaries and the Jews during that period had for its object the Khazar nation, part of whom had embraced Judaism.
2. The Kingdom of the Khazars
While Byzantium was pressing on the Euxine colonies from the west, endeavoring to draw them, together with the adjoining lands of the Slavs, into the sphere of Christian civilization, a new power from the east, from the Caucasus and the Caspian region, came rushing along in the same direction. We refer to the Khazars, or Kazars.[6] Forming originally a conglomerate of Finno-Turkish tribes, the warlike Khazars appeared in the Caucasus during the "migration of nations," and began to make inroads into the Persian Empire of the Sassanids, often acting as the tools of Persia's rival, Byzantium. The great Arabic conquests of the seventh century and the rise of the powerful Eastern Caliphate checked the movement of the Khazars towards the East, and turned it westward, to the shores of the Caspian Sea, the mouths of the Volga and the Don, the Byzantine colonies on the Black and Azov Seas, and, in particular, the flourishing region of Tauris. At the mouth of the Volga, where the mighty river joins the Caspian Sea, near the present city of Astrakhan, arose the kingdom of the Khazars with its capital Ityl, the name originally designating the river Volga. From there the bellicose Khazars made constant raids upon the Slavonian tribes far and near, to the very gates of Kiev, forcing them to become their tributaries.
Another Khazar center was established in the Crimea, among Byzantine Greeks and Jews. From the Crimea the Khazars pressed forward in the direction of Byzantium and the Balkan Peninsula, constituting a serious menace to the Roman Empire of the East. As a rule, the Byzantine emperors concluded alliances with the kings, or khagans, of the Khazars, checking their unbridled energy by means of concessions and the payment of tribute. In Constantinople the illusion was fostered that the Church, and with it Byzantine diplomacy, were in the end bound to triumph over all the Khazars—by converting them to Christianity. With this purpose in view, missionaries were dispatched from Byzantium, while the local bishops of Tauris were working zealously to the same end. But the task proved extremely difficult, for the Greek Church found itself face to face with a powerful rival in Judaism, which succeeded in establishing its hold on a part of the Khazar nation.
While yet in their pagan state, the Khazars were exposed at one and the same time to the influences of three religions: Mohammedanism, which pursued its triumphant march from the Arabic Caliphate; Christianity, which was spreading in Byzantium, and Judaism, which, headed by the Exilarchs and Gaons of Babylonia, was centered in the Caliphate, while its ramifications spread all over the Empire of Byzantium and its colonies on the Black Sea. The Arabs and the Byzantines succeeded in converting several groups of the Khazar population to Islam and Christianity, but the lion's share fell to Judaism, for it managed to get hold of the royal dynasty and the ruling classes.
The conversion of the Khazars to Judaism, which took place about 740, is described circumstantially in the traditions preserved among the Jews and in the accounts of the medieval Arabic travelers: