Danewirk

Also spelled  Danewerk,  Dannewirk , or  Dannewerk , Danish  Dannevirke , or  Danevirke (Danes' Bulwark)  the ancient frontier rampart of the Danes against the Germans, extending 10.5 miles (17 kilometres) from just south of the town of Schleswig to the marshes of the river Trene near the village of Hollingstedt. The rampart was begun about AD 808 by Godfred (Gudfred), king of Vestfold. In 934 it was penetrated by the German king Henry I, after which it was extended by King Harald I Bluetooth