along the Ob and Irtysh rivers. Around 1577, the Stroganovs hired the Cossack leader Yermak Timofeyevich to protect their lands from attacks of the Siberian Khan Kuchum . In 1580 Yermak started his conquest of Siberia. With some 540 Cossacks he started to penetrate territories that were tributary to Kuchum. Yermak