The Battle of Berestechko (Polish: Bitwa pod Beresteczkiem; Ukrainian: Берестецька битва, Битва під Берестечком) was fought between the Ukrainian Cossacks, led by Hetman Bohdan Khmelnytsky, aided by their Crimean Tatar allies, and a Polish–Lithuanian Commonwealth army under King John II Casimir. It was a battle of a Cossack rebellion in Ukraine that took place in the years 1648–1657 after the expiration of a two-year truce. Fought over three days from 28 to 30 June 1651, the battle took place in the province of Volhynia, on the hilly plain south of the Styr River. The Polish camp was on the river opposite Berestechko and faced south, towards the Cossack army about two kilometers away, whose right flank was against the River Pliashivka (Pliashova) and the Tartar army on their left flank.