The Russian conquest of Siberia began in July 1580 when some 540 Cossacks under Yermak Timofeyevich invaded the territory of the Voguls, subjects to Küçüm, the Khan of Siberia. They were accompanied by 300 Lithuanian and German slave laborers, whom the Stroganovs had purchased from the Tsar. Throughout 1581 this force traversed the territory known as Yugra and subdued Vogul and Ostyak towns. At this time they also captured a tax collector of Küçüm. Following a series of Tatar raids in retaliation against the Russian advance Yermak's forces prepared for a campaign to take Qashliq, the Siberian capital. The force embarked in May 1582. After a three-day battle on the banks of the river Irtysh, Yermak was victorious against a combined force of Küçüm Khan and six allied Tatar princes. On 29 Jun