The concluding phrases cast a shadow of doubt on the authenticity of this epistle or, more correctly, of some parts of both epistles, which more probably reflect the mournful Messianic temper of the sixteenth century, when this correspondence was brought to light by Spanish exiles who had made their way to Constantinople, than the state of mind of a Spanish dignitary or a Khazar king of the tenth century. However, the essential data contained in Joseph's epistle are so completely in accord with the reports of contemporaneous Arabic writers that the substance of this correspondence may be safely declared to be authentic.[14] Joseph's epistle must have arrived in Spain about 960. Only a few years later events occurred which made this King the last ruler of the Khazars. The apprehensions, voiced in his letter, concerning the Russians, with whom the King was at war, and who were ready to "destroy the whole land of the Ishmaelites as far as Bagdad," were speedily realized. A few years later the Slavonian tribes, who had in the meantime been united under the leadership of Russian princes, not only threw off the yoke of the Khazars, whose vassals they were, but also succeeded in invading and finally destroying their center at the mouth of the Volga. Prince Svyatoslav of Kiev devastated the Khazar territories on the Ityl, and, penetrating to the heart of the country, dislodged the Khazars from the Caspian region (966-969). The Khazars withdrew to their possessions on the Black Sea, and established themselves in particular on the Crimean Peninsula, which for a long time retained the name of Khazaria. The greatly reduced Khazar kingdom in Tauris, the survival of a mighty empire, was able to hold its own for nearly half a century, until in the eleventh century it fell a prey to the Russians and Byzantines (1016). The relatives of the last khagan fled, according to tradition, to their coreligionists in Spain. The Khazar nation was scattered, and was subsequently lost among the other nations. The remnants of the Khazars in the Crimea who professed Judaism were in all likelihood merged with the native Jews, consisting partly of Rabbanites and partly of Karaites.