 Initially it was the westernmost part of Mazovia within medieval Poland, especially after the fragmentation of Poland.According to German historiography, it is classified as part of Prussia, although it did not form part of pre-Christian Prussia and was not inhabited by the Old Prussians, but by Slavic Lechites, who in the 10th century became part of the emerging Polish state.The first historical account of Chełmno and Chełmno Land dates back to 1065 when Bolesław II of Poland granted a tax privilege to an abbey in a nearby Mogilno.