The vast nation, sometimes called Turks, sometimes Tatars, was distributed, according to all Oriental geographers, over all the countries of Northern Asia, from the river Jihun or Oxus to Kathay or China. That the Turks and the Arabs, both bent upon a persistent policy of conquest, should come into more or less hostile contact was inevitable. The struggle was a long one, and during the numerous engagements many prisoners were taken on both sides. Those Turks who fell into the hands of the Arabs were sent to the different provinces of their domain, where they became slaves of the chief emirs and of the caliphs themselves, where, finding favour in the eyes of the caliphs, they were soon transferred to their personal retinue. The distrust which the caliphs felt for the emirs of their court, whose claims they were only able to appease by making vassals of them, caused them to commit the grave error of confiding in these alien slaves, who, barbaric and illiterate as they were, now living in the midst of princes, soon acquired a knowledge of Muhammedanism, the sciences, and, above all, the politics of the country. It was not long before they were able to fill the most responsible positions, and, given their freedom by the caliphs, were employed by the government according to their abilities. Not only were they given the chief positions at court, but the government of the principal provinces was entrusted to them. They repaid these favours later by the blackest ingratitude, especially when the formation of a Turkish guard brought a number of their own countrymen under their influence. Ever anxious to augment his own body-guard, and finding the number of Turks he annually received as tribute insufficient, el-Mutasim purchased a great many for the purpose of training them for that particular service. But these youths speedily abused the confidence shown them by the caliph, who, perceiving that their insolence was daily growing more insupportable to the inhabitants of Baghdad, resolved to leave the capital, rebuild the ancient city of Samarrah and again make it the seat of the empire. At this time the captain of the caliph's guard was one Tulun, a freedman, whom fate would seem to have reduced to servitude for the purpose of showing that a slave might found a dynasty destined to rule over Egypt and Syria. Tulun belonged to the Toghus-ghur, one of the twenty-four tribes composing the population of Turkestan. His family dwelt near Lake Lop, in Little Bukhara. He was taken prisoner in battle by Nuh ibn Assad es-Samami, then in command at Bukhara. This prince, who was subject to the Caliph Mamun, paid an annual tribute of slaves, Turkish horses, and other valuables. In the year 815 a. d., Tulun was among the slaves sent as tribute to the caliph, who, attracted by his bearing, enrolled him in his own body-guard.