Nothing certain is known of the origin of the Cossack tribes, and no final agreement has been reached as to the derivation of their name. According to later supposition, their nucleus was a body of refugees from the ancient Russian lands invaded by Tartars in the thirteenth century. Some of those refugees settled between the embouchures of the Ural River, others near the mouth of the Don. Driven by invasion to form themselves into a military organization, the Cossacks of the Don became a formidable confederacy. Since 1549 they have been under the protection of Russia, and have rendered great service to the empire. Although they have always, since the time of Ivan IV, called the "Terrible" (1547-1584), furnished valorous soldiers to Russia, the Cossacks of the Don have often rebelled and disowned her authority. Russian troops have frequently been ordered to exterminate them. During the last years of Ivan IV these Cossacks entered upon that eastern conquest which led to Russian expansion into Asia. Karamzin, the Russian historian, is the most eminent authority on this subject. Among the enterprising leaders of the Cossacks at this time were Iermak Timofeif, John Koltzo--condemned to death by the Czar--James Mikhailoff, Necetas Pan, and Matthew Meschteriak, all noted for their rare intrepidity. The Stroganoffs, having heard of the terror inspired by their audacity among peaceful travellers, as well as amid the nomad tribes of the neighborhood, proposed an honorable service to these five brave men. On April 6, 1579, they sent them presents, accompanied by a letter in which they urged them to quit an occupation unworthy of Christian soldiers, to leave the class of brigands, and to become warriors of the White Czar, the monarch of Muscovy; to seek, in fine, dangers exempt from dishonor, by making peace with God and Russia. "We have," they added, "lands and fortresses, but few soldiers; come and defend great Perm and the Christian countries of the North." At these propositions Iermak and his companions shed tears of emotion. The hope of effacing their disgrace by glorious deeds, by services rendered to the State, the idea of exchanging the title of audacious brigands for that of brave defenders of their country, caused a keen sensibility in these men, uncouth, if you will, but with hearts still susceptible of remorse. Unfurling their standard on the bank of the Volga, they made an appeal to their comrades, and assembled five hundred fifty bold partisans, at the head of whom they arrived, burning with zeal, in the presence of the Stroganoffs, who received them with joy, as the annalist relates. The desires of the former, the promises of the latter, were realized. The Cossack leaders became the bucklers of the Christian country. The infidels trembled at the aspect of death which met them wherever they dared to show themselves. Indeed, on July 22, 1581, the