Boleslaus III, 1085–1138, duke of Poland (1102–38). The kingdom had been divided by his father, Ladislaus Herman, between Boleslaus and his elder brother Zbigniew, whose legitimacy was disputed. Zbigniew was supported by the Holy Roman emperor and other powers; however, Boleslaus defeated Zbigniew and reunited the kingdom. He routed (1109) Holy Roman Emperor Henry V at Hundsfeld and warred against Bohemia, Hungary, and Kiev. Having also regained Pomerania, which Mieszko II had lost to Denmark, Boleslaus entrusted the Christianization of its inhabitants to the bishop of Bamberg. In 1135 at Merseburg he signed a treaty with Holy Roman Emperor Lothair II, by which he received Pomerania and Rügen as fiefs of the empire. Vainly seeking to prevent the disintegration of his kingdom, Boleslaus altered the law of succession of his dynasty (see Piast). Among his sons, Casimir II was the most notable.