Chełmno (AUDPl-Chełmno.ogg'heUmno; older Culm; formerly ) is a town in northern Poland near the Vistula river with 18,915 inhabitants as of December 2021. It is the seat of the Chełmno County in the Kuyavian-Pomeranian Voivodeship.
Due to its regional importance in the Middle Ages, the city gave its name to the entire area, Chełmno Land (and later an administrative unit of the Kingdom of Poland, the Chełmno Voivodeship), the local Catholic diocese and Kulm law, which was used to found cities and towns around Poland, including the current capital city of Warsaw.
The city's name Chełmno comes from chelm, the old Polish word for hill. Culm was given to the first bishop of Prussia, Christian (d. 4 December 1245 in Marburg, Hessia), by Duke Konrad I of Masovia in 1222 and awarded to the Teutonic Order by Roman-German Emperor Friedrich II. in 1226. The Germanized name Culm/Kulm was used in official documents regarding the town, as the city was a member of the Hanseatic League and part of the State of the Teutonic Order. Chełmno was annexed by Prussia in the First Partition of Poland in 1772 and, as part of a larger Germanization effort, it was officially renamed Kulm. During the German occupation in World War II, the town was again renamed from Chełmno to Kulm.
The first written mention of Chełmno is known from a document allegedly issued in 1065 by Duke Bolesław II the Generous of Poland for the Benedictine monastery in Mogilno. In 1226 Duke Konrad I of Masovia invited the Teutonic Knights to Chełmno Land. In 1233 Kulm was granted city rights (German town law) known as "Kulm law" (renewed in 1251), the model system for over 200 German/Polish towns. The town was made the nominal see of the Roman Catholic Diocese of Chełmno under the archbishop of Riga by the papal legate William of Modena in 1243 (however, the cathedral and the residence of the bishop were located actually in the adjacent Chełmża). The town grew prosperous as a member of the mercantile Hanseatic League.
Kulm and Chełmno Land were part of the Teutonic Knights' state until 1454.