 In the 15th century, several changes were made to Silesia's borders.Parts of the territories which had been transferred to the Silesian Piasts in 1178 were bought by the Polish kings in the second half of the 15th century (the Duchy of Oświęcim in 1457; the Duchy of Zator in 1494).The Bytom area remained in the possession of the Silesian Piasts, though it was a part of the Diocese of Kraków.