In the Treaty of Choszczno (sometimes Treaty of Arnswalde), signed on 1 April 1269, the Brandenburgian Margraves of the House of Ascania John II, Otto IV and Conrad signed a treaty with Duke Mestwin II of Pomerania (Mściwój II) in Choszczno (Arnswalde). The treaty gave them rights in Pomerelia, including Świecie (Schwetz) and Białogard (Belgard).
In turn they had to finance the duke, e.g. for the marriage of Mestwin's daughter Katarzyna with Przybysław II of Parchim-Richenberg. In 1273 Mestwin paid Brandenburg feudal homage from the towns of Słupsk (Stolp) and Sławno (Schlawe). That way he was safe from his brother Wartislaw II of Pomerelia, because an attack on Mestwin would be considered as an attack on Brandenburg.
Through this treaty, the Margraviate of Brandenburg gained direct access to the Baltic Sea. In 1308, it also led to the Teutonic takeover of Danzig.[1]