Danewerk

The Danewerk was a wall between 12 and 20 feet in height built by the Danes to protect themselves from the Franks. It was built between the 8th and 10th century AD and stretched from the North Sea to the Baltic Sea, separating the Jutland Peninsula from the northern extent of the Franks' empire. The wall was destroyed in 1864 after its capture by the Austrians and Prussians.