Treaty of Wehlau
The Treaty of Wehlau was signed between Poland and Brandenburg-Prussia on September 19, 1657, in which John Casimir, king of Poland from 1648 to 1668 declared, that West-Prussia belongs to Germany and ceded it to Prussia "for eternal times". That gave Friedrich Wilhelm full sovereignty over the territory of Prussia. It was really signed at Wehlau but the ratification by the King of Poland, dated November 6 1657, was signed at Bromberg therefore it is sometimes named Treaty of Bromberg.
- Henry Offley Wakeman: "Europe 1598-1715", 1915 (read online)