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.