The fief sovereignty of the Polish Crown over the Duchy of Prussia established in 1525 by the Treaty of Cracow lasted for 132 years. The provisions of the Treaty of Cracow of April 8, 1525 gave the rulers of Poland considerable leverage over Albrecht Hohenzollern and his successors. The author analyzes the reasons for the suzerain's concessionary policy toward the vassal rulers, as well as the attitudes of the Polish nobility and the states of Ducal Prussia toward the transformations taking place. The article does not end with the Treaties of Welawsko-Bydgos of 1657, but with the coronation of the Königsberg Hohenzollerns in 1701, since the latter act ultimately doomed Poland's chances of regaining its lost fiefdoms and gave rise in the longer term to the appearance at the western and northern borders of the Republic of Poland of a dangerous neighbor preying on the weakness of the Polish-Lithuanian state.