Kwidzyn (German Marienwerder) is town in northern Poland on Liwa River, with 39,300 inhabitants (1995). Situated in the Pomeranian Voivodship since 1999, previously in Elblag Voivodship (1975-1998).
Among its important monuments is the Gothic castle of Pomezanian bishops from 14th c., modelled on Teutonic Knights' castles, partly pulled down in 1789. From east a cathedral church is connected with castle.
After World War I, the Versailles Treaty returned most of West Prussia to Poland. However, much of the area's population was ethnically German, and so a plebiscite was held on 11 July 1920. 92% of the inhabitants chose the Kingdom of Prussia, and the district was placed under German control 16 August.