The Battle of Prostken was fought near Prostken, Duchy of Prussia (today Prostki in Ełk County, Poland) on October 8, 1656 between forces of the Polish-Lithuanian Commonwealth and allied Crimean Tatars commanded by hetman Wincenty Gosiewski on one side, and on the other allied Swedish and Brandenburg forces commanded by Prince Georg Friedrich of Waldeck, reinforced by cavalry of Prince Bogusław Radziwiłł. The Commonwealth forces won the battle, annihilating enemy forces and taking Radziwiłł captive.