 When this area was subdued by the rulers of the Polans Chełmno became a local centre of castellany (kasztelania).Chełmno Land was Christianised in the 11th century.According to the will of Duke Bolesław III Wrymouth, Chełmno Land, after his death in 1138 became a part of the Duchy of Masovia governed by his son Bolesław IV the Curly and his descendants during the feudal fragmentation of Poland.