In the early part of the fourteenth century Othman, a Mongol, founded the Ottoman empire, which then consisted of only the western part of Asia Minor. His son and successor conquered Gallipoli in 1354, thereby gaining a foothold in Europe, and during the next two centuries successive Turkish rulers made large additions to the empire until it embraced vast areas in Europe, Asia, and Africa. For a time, indeed, it threatened to absorb all Christendom. Adrianople was conquered in 1361 and made the capital of the Turkish Empire. Then, in 1453, after a memorable siege, Constantinople was captured by the Muhammadans, and made the capital of the empire. Orkhan was the first to exact as tribute the strongest and healthiest male children of all Christian peoples whom he conquered. These youths, reared as Muhammadans and trained under strict military discipline, became that efficient body of troops called the Janizaries. For a long time they were the bulwark of the empire, but at length they became so dictatorial and powerful that the sultan began to fear them more than he feared his foreign enemies. In 1825, when the army was reorganized on the European plan, the Janizaries broke out in open revolt. Then the reigning sultan unfurled the flag of the Prophet and called upon the faithful to suppress the rebellious corps. In the contest that ensued it is estimated that twenty-five thousand of the rebels were put to death, twenty thousand were banished, and the others disbanded. This was the end of an epoch of blood-shedding and the beginning of an era of commerce. The Russians have always been noted for their love of furs; as a result a small, fur-bearing animal, the sable, led to the conquest of that vast realm now known as Siberia. About the middle of the sixteenth century a rich Russian merchant named Strogonoff, residing at Kazan, established salt works on the banks of the Kama, a tributary of the Volga River, and began trading with the natives. One day, having noticed some strangely dressed travellers and learning that they came from a country beyond the Ural Mountains, called Sibir, he despatched some of his agents into that land. On returning, the employees brought with them the finest sable skins that the merchant had ever seen. They had been secured for a trifling sum. Strogonoff began at once to extend the area of his trafficking, and informed the government of the lucrative commerce that he had opened up. Valuable concessions were then granted him. A few years afterward a Cossack officer named Yermak, who had been declared an outlaw by Ivan the Terrible, gathered together a force of less than one thousand men. The band was composed of adventurers, freebooters, and criminals, and the expedition was armed and provisioned by Strogonoff, who expected to profit by opening up the new region. Permission having been obtained from the government, in 1579 Yermak set forth with his followers for the unknown country.