After the war , the town was transferred to Poland under border changes promulgated at the Potsdam Conference . Its surviving German residents who had not evacuated were subsequently expelled westward and replaced with Poles , most of whom were themselves expelled from the pre-war Polish Vilnius Region . The town was given the historic Polish name '' Rastembork '' in 1945 , and in 1946 it was renamed to '' Kętrzyn '' after the Polish historian Wojciech Kętrzyński . Both names are still commonly used nowadays , with Rastembork being more popular among ethnic Masurians and foreigners . After the war , the town 's life was being rebuilt . In 1945 , the Municipal Theater was established . Thanks to voluntary contributions , books were purchased for newly organized public libraries . A museum was created in the renovated castle
Potsdam Conference
Potsdam Conference
Kętrzyn