In tsarist Russia, the term serf (Russian: крепостной крестьянин, romanized: krepostnoy krest'yanin, lit. 'bonded peasant') meant an unfree peasant who, unlike a slave, originally could be sold only together with the land to which they were "attached". However, this had stopped being a requirement by the 19th century, and serfs were by then practically indistinguishable from slaves. Contemporary legal documents, such as Russkaya Pravda (12th century onwards), distinguished several degrees of feudal dependency of peasants. While another form of slavery in Russia, kholopstvo, was ended by Peter I in 1723, serfdom (Russian: крепостное право, romanized: krepostnoye pravo) was abolished only by Alexander II's emancipation reform of 1861; nevertheless, in times past, the state allowed peasants to sue for release from serfdom under certain conditions, and also took measures against abuses of landlord power.
Serfdom became the dominant form of relation between Russian peasants and nobility in the 17th century. Serfdom most commonly existed in the central and southern areas of the Tsardom of Russia and, from 1721, of the subsequent Russian Empire. Serfdom was rare in Little Russia (parts of today's central Ukraine), other Cossack lands, the Urals and Siberia until the reign of Catherine the Great (r. 1762–1796), when it spread to Ukraine; noblemen began to send their serfs into Cossack lands in an attempt to harvest their extensive untapped natural resources.
