^John Freely Celestial Revolutionary: Copernicus, the Man and His Universe 2014 - - 0857734903 p 6
The Peace of Thorn was reaffirmed on 8 April 1525 by the Treaty of Krakow, which gave the Grand Master of the Teutonic Knights hereditary possession of the Order's territory, then known as 'Ducal Prussia', as a fief of the Polish Crown.