The original settlement founded at the mouth of the Weser on the North Sea became a bishopric in the 8th century. The township’s importance began to grow in the 9th century, when the archbishopric was moved from nearby Hamburg. Bremen received its charter as a town in 1186 from Frederick I, a step which enabled its further economic development. In the 16th century the citizens of Bremen attached themselves to the reformation movement, and in 1646 Bremen was declared a city-state. From 1815, as the Free Hanseatic City, it was a member of the German Federation, and since 1920 has been one of the Läender of Germany.