Silesia, Lesser Poland, Greater Poland, Masovia, Pommerania, Sieradz and Łęczyca were part of the Polish Seniorat between 1138 and the 1320 century. In 1138 Bolesław III. devided the Kingdom of Poland between his sons. Each of them got a duchy which was ruled by him but was dependent to the Senior of Poland, the duke of Kraków. In 1320 Władysław I. reestablished the Kingdom of Poland by uniting Lesser Poland and Greater Poland.