The Ural range had hitherto been the eastern boundary of Russia. Beyond lay a region of steppes and rivers, peopled towards the polar seas by tribes of Tartar and Esquimaux origin, employed in hunting; and on the southern frontier, by Kirghiz and Kalmak nomads. Under Vassili III. (1505–1533) the Western Urals were annexed to the nascent empire, and peopled by Yaik Cossacks, a race addicted to raiding and pillage.[532] These freebooters recognised no natural barriers. Crossing the mountain-chain, they attacked the Ostiaks, Samoyeds, and Kirghiz who had hitherto roamed unchallenged over the wind-swept plains. The collision was disastrous for the invaders, and the frontier became a prey to anarchy. Meantime the Tsar, Ivan the Terrible, had bestowed a huge tract of land in the Urals on his favourite, Strogonoff, who at once began to exploit its rich deposits of gold. His schemes were rendered abortive by the incursions of tribesmen from the west, and Strogonoff, in despair, summoned a Cossack named Iermak to his aid. The new ally was promised a free pardon for his numerous outrages, and his followers were supplied with firearms from Russian arsenals. Thus equipped Iermak made short work of the invaders, and in 1587 captured Sibir, the capital of Kushan Khān, chief of the Kirghiz. In 1604 Tobolsk was built and fortified on a site twelve miles from the town which gave its name to the entire country. The victorious Cossacks plunged deeper into the hitherto unknown regions, and came to blows with the Kirghiz, who ranged the steppes between Lake Balkash and the Urals on the northern shore of the Aral Sea. Hearing vague rumours of the wealth of Khiva or Khwārazm, a Khānate embracing the fertile embouchure of the Amū Daryā, a band of Cossacks swooped down on Urgenj, its capital, at a time when the Khān and his warriors were absent on a distant expedition.