The state was established between 1248 and 1264, with duke Mestwin II being given the lands by his father, Swietopelk II, from the Duchy of Gdańsk.[1] He was originally given the lands around Raciąż and Szczytno, and around 1264, he incorporated into his territories Świecie, conquered from the Duchy of Kuyavia, which become the capital of the state.[2] In 1269, it incorporated the Duchy of Lubiszewo, and the year later, in 1270, it conquered the Duchy of Gdańsk, uniting its lands into the Duchy of Pomerelia.[3]
