Originally peasants (primarily Ukrainian and Russian) who fled from bondage to the lower Dnepr and Don river regions to settle in the frontier areas separating fifteenth-century Muscovy, Poland, and the lands occupied by the Tatars. They later organized themselves into military formations to resist Tatar raids. Renowned as horsemen, they were absorbed into the army of the Russian Empire (q.v.) by the late eighteenth century. In the early 1990s, there were attempts to reestablish a Cossack military tradition in Ukraine.