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. 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. From 1560 Bielsko was held by Frederick Casimir of Cieszyn, son of Duke Wenceslaus III Adam, who due to the enormous debts his son left upon his death in 1571, had to sell it to the Promnitz noble family at Pless. With the consent of Emperor Maximilian II, the Promnitz dynasty and their Schaffgotsch successors ruled the Duchy of Bielsko as a Bohemian state country; acquired by the Austrian chancellor Count Friedrich Wilhelm von Haugwitz in 1743, and afterwards by Polish aristocrat Aleksander Józef Sułkowski in 1752, the ducal status was finally confirmed by Empress Maria Theresa in 1754. It remained in possession of the Polish Sułkowski family until the dissolution of the duchy in 1849, while the castle was still owned by the Sułkowskis until World War II. After the Prussian king Frederick the Great had invaded Silesia, Bielsko remained with the Habsburg monarchy as part of Austrian Silesia according to the 1742 Treaty of Breslau. In late 1849 Bielsko became a seat of political district. In 1870 it became a statutory city. Biała The opposite bank of the Biała River, again Polish since 1454, had been sparsely settled since the mid-16th century. A locality was first mentioned in a 1564 deed, it received the name Biała in 1584, and belonged at that time to Kraków Voivodeship. Its population increased during the Counter-Reformation in the Habsburg lands, when many Protestant artisans from Bielsko moved across the river. Though already named a town in the 17th century, Biała officially was granted city rights by the Polish king Augustus II the Strong in 1723. In the course of the First Partition of Poland in 1772, Biała was annexed by