"Bolesław II of Masovia or Bolesław II of Płock (pl: Bolesław II mazowiecki (płocki); ca. 1253/58 – 20 April 1313), was a Polish prince member of the House of Piast, Duke of Masovia during 1262-1275 jointly with his brother, since 1275 sole ruler over Płock, since 1294 ruler over all Masovia and Duke of Kraków and Sandomierz during 1288-1289. In 1310 he gave to his sons the districts of Warsaw and Czersk." - (Wikipedia (en) 28.10.2019)
de