Wikipedia
Hedeby (, Old Norse Heiðabýr, German Haithabu) was an important Viking Age (8th to the 11th centuries) trading settlement near the southern end of the Jutland Peninsula, now in the Schleswig-Flensburg district of Schleswig-Holstein, Germany. It is the most important archaeological site in Schleswig-Holstein by far. The Haithabu Museum was opened next to the site in 1985.
The settlement developed as a trading centre at the head of a narrow, navigable inlet known as the Schlei, which connects to the Baltic Sea. The location was favorable because there is a short portage of less than 15 km to the Treene River, which flows into the Eider with its North Sea estuary, making it a convenient place where goods and ships could be ported overland for an almost uninterrupted seaway between the Baltic and the North Sea and avoid a dangerous and time-consuming circumnavigation of Jutland, providing Hedeby with a role similar to later Lübeck. Hedeby was the second largest Nordic town during the Viking Age, after Uppåkra in southern Sweden, The city of Schleswig was later founded on the other side of the Schlei. Hedeby was abandoned after its destruction in 1066.
The site came to be located in the Duchy of Schleswig, which was traditionally the personal territory of the kings of Denmark. The Kingdom of Denmark lost the area to Austria and Prussia in 1864 in the Second Schleswig War, and inhabitants of the area opted to remain with Germany in the Schleswig plebiscites of 1920. Hedeby used to be the oldest city in Denmark until its loss to Prussia.