Indigenous peoples of Siberia – notably the Yakuts and the Buryats of Eastern Siberia – practised slavery on a small scale. With the conquest of Siberia in the 16th and 17th centuries, Russians enslaved natives in military operations and in Cossack raids. Cases involving native women were frequent, held as concubines, sometimes mortgaged to other men and traded for commercial profit. The Russian government generally opposed the conversion of natives to Christianity because it would free them from paying the yasak, the fur tribute. The government decreed that the non-Christian slaves were to be freed. This in turn led local Russian owners of slaves to petition the government for conversion and even involved forced conversions of their slaves. The rules stipulated that the native convert became a serf of the converter. As an indication of the extent of the slavery system, one voyevoda reported in 1712 that "there is hardly a Cossack in Yakutsk who does not have natives as slaves".