involved him in a long and ultimately dangerous war with the Chagan of the Avars, a Tartar tribe newly established on the north bank of the lower Danube, whom Justinian had paid to keep off the Huns and other troublesome neighbours. The Avars, originally a race of no great importance, obtained at this moment a great extension of power and territory by allying themselves with the Lombards, in order to destroy the Gepidae, the Gothic tribe who dwelt north of Sirmium on the middle Danube. After exterminating their Teutonic neighbours, the Lombards passed on to invade Italy,[21] and left the Avars in possession of the whole line of the Danube, from Vienna to its mouth. Thenceforth the Avars were a scourge to the already half-desolate provinces of Moesia and Illyricum. They ranged over the whole territory up to the Balkans, in spite of the innumerable fortresses which Justinian had built and garrisoned to defend the Danube bank. This trouble was continually growing worse all through the reign of Justin II., and became an actual source of danger, as well as of mere annoyance, in the time of his successors. Footnote 21: See p. 181. Another refusal of Justin to make a payment of money, which he considered degrading to his majesty, was destined to bring on a struggle even more ruinous than that with the Avars. It will be remembered that the peace between Justinian and Chosroes of Persia, concluded in 562, had stipulated for some payments from the East-Romans to the king. In 571 Justin refused to fulfil his obligations, and plunged the empire into a wholly unnecessary war with his great Oriental neighbour. Several causes conspired to induce Justin to undertake this struggle. He was implored by the Christian population of Persian Armenia to deliver them from the fire-worshipping Sassanians, and the Turks of the Oxus had sent an embassy to promise him help from the East if he would assault Chosroes. Dizabul, their great Khan, engaged to distract the forces of the enemy by crossing the Oxus and invading northern Persia, while Justin’s generals were to cross the Tigris and attack Media.