sentences:  The Biała again became a border river, when in 1315 the eastern Duchy of Oświęcim split off from Cieszyn as a separate under Mieszko's son Władysław.After the Dukes of Cieszyn had become vassals of the Bohemian kings in 1327 and the Duchy of Oświęcim was sold to the Polish Crown in 1457, the Biała River for centuries marked the border between the Bohemian crown land of Silesia within the Holy Roman Empire and the Lesser Polish region of the Kingdom of Poland and the Polish–Lithuanian Commonwealth.With Bohemia and the Upper Silesian Duchy of Cieszyn, Bielsko in 1526 was inherited by the Austrian House of Habsburg and incorporated into the Habsburg Monarchy.