Duchy of Oświęcim
After the partition of the Duchy of Opole in 1281, Bielsko passed to the Dukes of Cieszyn within fragmented Poland. The town was first documented in 1312 when Duke Mieszko I of Cieszyn granted a town charter. 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, returning to Lesser Poland after three centuries, the Biała River for next centuries marked the border between the Bohemian crown land of Silesia within the Holy Roman Empire and the Lesser Poland Province of the Kingdom of Poland and the Polish–Lithuanian Commonwealth.