As the westernmost clan, the Pomesanians were the first of the Prussians to be conquered by the Teutonic Knights, a German military crusading order brought to the Chełmno Land to convert the pagans to Christianity.

The territory is said in folk etymology to have been named after Pomeso, a son of Widewuto, legendary chieftain of the Prussians.

Georg Gerullis determined that its name was actually derived from the Old Prussian word pomedian, meaning fringe of the forest.

In 1233 the work began in Marienwerder (Kwidzyn), and during the winter the Prussians gathered a large army for a major battle on the Sirgune (Dzierzgoń) River, where they suffered a great defeat.

In 1243, the Bishopric of Pomesania was established and put under the jurisdiction of the Archbishop of Riga by papal legate William of Modena.

As the westernmost Prussian territory, it was the most exposed clan to the Polish Pomeranian, Masovian, and Kuyavian and then German colonists and their cultures.