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.