The Duke of Silesia was the sons and descendants of the Polish Duke Boleslaw III Wrymouth. In accordance with the last will and testament of Boleslaw, upon his death his lands were divided into four or five hereditary provinces distributed among his sons, and a royal province of Kraków reserved for the eldest, who was to be High Duke of all Poland. This was known as the fragmentation of Poland. Subsequent developments lead to further splintering of the duchies.