 The Seniorate Province was supposed to be ruled by the rotating head of the royal Piast dynasty, a principality that he held as overlord (Senior Prince or High duke, "princeps") of the other Polish dukes.The senioral principle established in the testament stated that at all times the eldest member of the dynasty was to have supreme power over the rest ("Dux", the Dukes) and was also to control an indivisible "Seniorate Province".In 1138 Bolesław's III eldest son Władysław II, took up the rule over a vast strip of land running north–south down the middle of Poland, composed of