For years, this Greek empire at Constantinople had been obliged to fight hard against the Mohammedans who came swarming across the fertile plains of Mesopotamia (mĕs′ō pō tā′ mĭ ā) and Asia Minor. (Mesopotamia is the district lying between the Tigris (tī′grĭs) and Euphrates (ūfrā′tēz) Rivers. Its name in Greek means “between the rivers.”) The fiercest of the Mohammedan tribes, the warlike Ottoman Turks, were the last to arrive. For several years, they thundered at the gates of Constantinople, while the Greek Empire grew feebler and feebler. At last in 1453, their great cannon made a breach in the walls, and the Turks poured through. The Greek Empire was a thing of the past, and all of southeastern Europe lay at the mercy of the invading Moslems (another name for “Mohammedans”). The Turks did not drive out the Greeks, Bulgarians, Serbians, and Albanians, but settled down among them as the ruling, military class. They strove to force these peoples to give up Christianity and turn Mohammedans, but were successful only in the case of the Skipetars of Albania. The Albanians, Serbians, Bulgarians, Greeks, and Roumanians remained where they had been, but were oppressed by the newcomers. For more than two hundred years after the capture of Constantinople, the Turks pushed their conquests farther and farther into Europe. The entire coast of the Black Sea fell into their hands. All of Greece, all of Bulgaria, and all of Roumania became part of their empire. Of the kingdom of Serbia, one small province remained unconquered. Up in the mountains near the coast of the Adriatic gathered the people of one county of the Serbian kingdom. As the Turks attacked them, they retreated higher and higher up the mountain sides and rolled huge stones down upon the invaders. Finally, the Turk became disgusted, and concluded that “the game was not worth the candle.” Thus the little nation of Montenegro was formed, composed of Serbians who never submitted to the Ottoman rule. (The inhabitants of this small country call it Tzernagorah (tzẽr nä gō′ra); the Italians call it Montenegro. Both of these names mean “Dark Mountain.”) Not satisfied with these conquests, the Turks pushed on, gaining control of the greater part of the kingdom of Hungary. About 1682, they were pounding at the forts around Vienna. The heroic king of Poland, John Sobieski (sō bĭ ĕs′kĭ), came to the rescue of the Austrian emperor with an army of Poles and Germans and completely defeated the Turks. He saved Vienna, and ended any further advance of the Turkish rule into Europe. (The map on page 82 shows the high water mark of the Turkish conquests.)