January 1, 1138
Testament of Bolesław III Wrymouth
Bolesław III Wrymouth's Testament of 1138 introduced the principle of seniority and divided the Polish state among the ruler's sons. This event initiated the period of feudal fragmentation in Poland, which lasted almost 200 years and ended with the coronation of Władysław the Elbow-high in 1320. This decision significantly influenced the fate of medieval Poland.
