Słupsk developed from a few medieval settlements located on the banks of the Słupia River, at the unique ford along the trade route connecting the territories of modern Pomeranian and West Pomeranian Voivodeships. This factor led to the construction of a grod, a West Slavic or Lechitic fortified settlement, on an islet in the middle of the river. Surrounded by swamps and mires, the fortress had perfect defence conditions. Archaeological research has shown that the grod was situated on an artificial hill and had a natural moat formed by the branches of the Słupia, and was protected by a palisade. Records confirm that the area of Słupsk was part of the Polish realm during the reign of Mieszko I and in the 11th century.