Schleswig is situated at the end of the Schlei, an arm of the Baltic sea. Merchants settled on the south bank of the Schlei in the 9C. Located at the crossroads of the old north-south road to Jutland and the Baltic-North Sea overland route, the settlement soon prospered. A century later, Viking invaders created the Haithabu («the town in the heather»). In the 11C, marauding Scandinavian pirates forced the townspeople to move to the north bank of the Schlei, where they founded the town of Schleswig.