Meanwhile the Muslim empire had arisen. The Persian em pire was struck down (637), and the Muslims poured into Ar menia. The khakan, who had defied the summons sent him by the invaders, now aided the Byzantine patrician in the defence of Armenia. The allies were defeated, and the Muslims under took the subjugation of Khazaria (651). Eighty years of war fare followed, but in the end the Muslims prevailed. The khakan and his chieftains were captured and compelled to embrace Islam (737), and till the decay of the Mohammedan empire Khazaria, with all the other countries of the Caucasus, paid an annual tribute of children and of corn (737-861). Nevertheless, though overpowered in the end, the Khazars had protected the plains of Europe from the Mohammedans and made the Caucasus the limit of their conquests.
In the interval between the decline of the Mohammedan empire and the rise of Russia, the Khazars reached the zenith of their power. The merchants of Byzantium, Armenia and Bagh dad met in the markets of Itil (whither, since the raids of the Mohammedans, the capital had been transferred from Semender) and traded for the wax, furs, leather, and honey that came down the Volga. So important was this traffic held at Constantinople that, when the portage to the Don was endangered by the irrup tion of a fresh horde of Turks (the Petchenegs), the emperor, Theophilus, himself despatched the materials and workmen to build for the Khazars a fortress impregnable to their forays (834). Famous as the one stone structure in that stoneless region, the post became known far and wide amongst the hordes of the steppe as Sar-kel or the White Abode. Merchants from every nation found protection and good faith in the Khazar cities. The Jews, expelled from Constantinople, sought a home amongst them, developed the Khazar trade, and contended with Moham medans and Christians for the theological allegiance of the Pagan people. The dynasty accepted Judaism (c. 740), but there was equal tolerance for all, and each man was held amenable to the authorized code, and to the official judges of his own faith. At the Byzantine court the khakan was held in high honour. The em peror, Justinian Rhinotmetus, took refuge with him during his exile and married his daughter (702). Justinian's rival, Vardanes, in turn sought an asylum in Khazaria, and in Leo IV. (775) the grandson of a Khazar sovereign ascended the Byzantine throne. Khazar troops were amongst the bodyguard of the imperial court ; they fought for Leo VI. against Simeon of Bulgaria; and the khakan was honoured in diplomatic intercourse with the seal of three solidi, which marked him as a potentate of the first rank, above even the pope and the Carolingian monarchs. Indeed, his dominion became an object of uneasiness to the jealous statecraft of Byzantium, and Constantine Porphyrogenitus, writing for his son's instruction in the government, carefully enumerates the Alans, the Petchenegs, the Uzes, and the Bulgarians as the forces he must rely on to restrain it.
It was, however, from a power that Constantine did not con sider, that the overthrow of the Khazars came. The arrival of the Varangians amidst the scattered Slays (862) had united them into a nation. The advance of the Petchenegs from the East gave the Russians their opportunity. Before the onset of those fierce invaders the precarious suzerainty of the khakan broke up. By calling in the Uzes, the Khazars did, indeed, dislodge the Petchenegs from the position they had seized in the heart of the kingdom, between the Volga and the Don, but only to drive them inwards to the Dnieper. The Hungarians, severed from their kindred and their rulers, migrated to the Carpathians, whilst Oleg, the Russ prince of Kiev, passed through the Slav tribes of the Dnieper basin with the cry "Pay nothing to the Khazars" (884). The kingdom dwindled rapidly to its ancient limits be tween the Caucasus, the Volga, and the Don, whilst the Russian traders of Novgorod and Kiev supplanted the Khazars as the carriers between Constantinople and the North. When Ibn FacIlan visited Khazaria 4o years later, Itil was even then a great city, with baths and market places and 3o mosques. But there was no domestic product or manufacture; the kingdom depended solely upon the now precarious transit dues, and administration was in the hands of a major domus also called khakan. At the assault of Swiatoslav of Kiev the rotten fabric crumbled into dust. His troops were equally at home on land and water. Sarkel, Itil, and Semender surrendered to him (965-969). He pushed his conquests to the Caucasus and established Russian colonies upon the Sea of Azov. The principality of Tmutarakan, founded by his grandson, Mstislav (988), replaced the kingdom of Khazaria, the last trace of which was extinguished by a joint expedition of Russians and Byzantines (I oi 6).
Modern: Klaproth, "Mem. sur les Khazars," in Journ. As., 1st series, vol. ib., Tableaux hist. de l'Asie (1823) ; ib., Tabl. hist. de Caucasus (1827) ; memoirs on the Khazars by Harkavy ; and by Howorth Congres intern. des Orientalistes, vol. ii.; D'Ohsson, Peuptes du Caucase (1828) ; S. Krauss, "Zur Geschichte der Chazaren," in Revue orientate pour les etudes Ourals-altaiques (1900).