The Strogonofs, once established on the Kama, experienced, as generally happens when a civilized people finds itself in contact with barbarous tribes, the necessity of extending further eastwards at the expense of their Tatar neighbours, if only to protect themselves from their depredations. In 1581 the Tsar gave them permission to employ a celebrated Cossack pirate, Ermak Timoféef,[7] who seized the city of Sibir, or Isker, then capital of Khan Kuchun, the principal Tatar chief of Western Siberia. Six years later the present city of Tobolsk rose on the site of Sibir. We will not attempt to narrate the history of the conquest of Siberia, which strongly resembles the taking of North America by French pioneers at about the same time. When the Tatar tribes of the West had been driven towards the Southern Steppes, the Cossacks encountered little opposition from the poor hunters and fishermen whom they found in the district. In summer these Cossack adventurers navigated the rivers in canoes, whilst their winters were spent in block-houses, or _ostrogs_, surrounded by palisades not unlike the forts erected by the Hudson Bay Company. Soon they became very numerous, being attracted from the more civilized parts of Russia by the growing profits of the fur trade. In 1636 they had reached the mouth of the Yenissei, and a year later arrived on the banks of the Lena. In less than two years—that is, in 1639—they had discovered the shores of the Okhotsk, and fifty years later the whole continent had been traversed from end to end. In 1648 the Cossack adventurers Alexief and Dezhnief doubled the eastern extremity of Asia, and arrived at Kamtchatka, and in 1651 the Ataman Khabarof established himself on the Amur, where he discovered other adventurers, who had already descended this river in 1643. At this juncture the Russians found themselves face to face with the Manchus, who had just conquered China, and notwithstanding the heroic defence of their fortress at Albazine on two occasions, they were obliged in 1688 to abandon the middle and lower basins of the Amur to the Sons of Heaven in accordance with the treaty of Nertchinsk, a territory which they only reconquered from the degenerate Chinese in 1858.