The close of the sixteenth century therefore fixed the limits of Turkish advance. The opening years of the seventeenth century marked the first beginnings of Turkish retreat. By the treaty of Sitvatorok, concluded between the Emperor and the Sultan in 1606, the annual tribute of 30,000 ducats agreed to be paid by the Emperor for the portion of Hungary which he still retained under his own government was abolished. From that day to the present the history of the Ottoman Turks in Europe has been that of a gradual but steady decline in the strength of their authority over south-eastern Europe. In the seventeenth century the struggle was for the possession of the valley of the Danube. The contest was a severe one. The Turks fought more strenuously for the command of the Danube than they did for Greece or Bulgaria. Bit by bit with many changes of fortune they were slowly driven back, until soon after the end of the century not an acre of land on the northern bank of the river between the Theiss and the Pruth was still in their possession. Since then the work of liberation has progressed steadily but slowly. One by one the Crimea, Wallachia, Moldavia, Bessarabia, Servia, Greece, Bosnia, and Bulgaria have been won back by Christendom from the rule of the Turk, either to complete independence or to subjection to a neighbouring Christian power. But just as it was the mutual disunion of Christian powers which enabled the Turks to conquer south-eastern Europe so easily in the fifteenth and sixteenth centuries, so it has been the mutual jealousy of Christian powers which has made the task of emancipation so slow and so difficult in the nineteenth century. For many years the Ottoman Sultans have lived in Europe on sufferance, because it has seemed a lesser evil to the great powers of Europe to retain the Turk than to aggrandise the Czar. [Sidenote: =Antagonism to the House of Austria.=]