Duke Bolesław III died on 28 October 1138. In his will, he sought to maintain the unity under the Polish crown of the conquered neighbouring lands as well as to prevent inheritance conflicts among his sons. He therefore determined a kind of mitigated primogeniture principle: As the oldest son, the supreme authority in the country was assigned to Władysław with the title of a High Duke ("Princeps"). In addition to Silesia, he received the central Seniorate Province, stretching from Lesser Poland at Kraków to eastern Greater Poland and western Kuyavia, as well as the authority over the Pomerelian lands at Gdańsk on the Baltic Sea. His younger half-brothers Bolesław IV the Curly and Mieszko III received the eastern Duchy of Masovia (composed of Masovia with eastern Kuyavia) and the western Duchy of Greater Poland (the remaining parts of Greater Poland with Lubusz Land) respectively, each as hereditary fiefs.