Culmland or Chelmno Land - (Polish: Ziemia Chelminska, German: Kulmerland) is a traditional name for the district around the city of Chełmno (German: Kulm or Culm) in northern Poland. Other German forms of the names are Kulmer Land, Culmerland or Culmer Land.
It is located on the right bank of the Vistula river, from the mouth of the Drwęca (German Drewenz) river to Chelmno. Where the Vistula river takes a sharp turn northward, the Drwęca forms the eastern border of the region, while its southern and western border is the Vistula river.
In the Middle Ages the region was a part of Masovia, being subject to constant raids of the pagan Prussians. To protect his land from invasions, duke Conrad I of Masovia called upon the Teutonic Knights for help. They were to keep the Culmland as a fief in exchange for protecting Mazovia from pagan Prussians, though some allege the grant to be a forgery. The Teutonic Order obtained a Papal bull and an Imperial bull of the Emperor Frederick II before entering Prussia.
In 1243 Prussia was divided by the papal legate William of Modena into four dioceses under the archbishop of Riga. The four parts were called Culmland, Pomesania, Warmia (Ermland) and Sambia (Samland). Chelmno and Toruń (then called Thorn), at the Vistula river and north of the Drwęca river, lay on the border with Masovia.
Poland was able to recover this land in 1466 after the Thirteen Years War against the Teutonic Knights, when the Second Treaty of Thorn placed it under the Polish crown as a part of Royal Prussia.