After the death of Dušan Silni the great Serbian Empire crumbled into a large number of small states, whose rulers played a dangerous game, and intrigued one against the other, whilst the Turks were conquering Thrace. The Macedonian despots became vassals to the Turks, and only a few countries like Zeta, Bosnia, and the empire of Prince Lazar (the Serbia of to-day) maintained their independence. So long as these countries were free, the Ottoman invasion of Europe was delayed, because in the Kossovo polje (the field of Kossovo) Serbia held the key of Europe. The Turks knew this and constantly prepared their attacks accordingly. On Vidovdan (St. Vitus Day, 1387) 100,000 Serbs and 300,000 Turks met in battle on the Kossovo. The battle was fierce and the losses on both sides were enormous. The Serbs lost their Prince Lazar and all their nobility; the Turks the greater part of their army and their Sultan Murat I. In Europe the report spread that the Serbs had been victorious; in Florence and Paris all the bells were rung for joy, and a service of thanksgiving was held in Notre Dame, which was attended by Charles VI. with all his Court. Murat’s successor, Bayazit did not penetrate further; he permitted the Serbs to retain their own laws, but they had to acknowledge him as their suzerain. In 1459 Serbia was finally crushed and fell completely under Turkish rule. Soon after (1463) the same fate befell Bosnia and Hercegovina. Only the mountain fastnesses of Montenegro remained unconquered. III.