Danevirke, also known as Dannevirke or Danewerk, means "Dane's work". It is the name for the Danish earthen defense structure, which stretches from the swampy moors of west Jutland to the town of Schleswig, situated at Slien at the Baltic Sea, near the Viking trade centre of Hedeby.
According to written sources, the work on Danevirke was initiated by the Danish King Godfred in 808 AD. Fearing an invasion by the Franks, Godfred commenced the work of an enormous structure for the defense of his realm, which separated the Jutland Peninsula from the northern extent of the Frankish empire.
In 1969-75 three building phases of the main structure of Danevirke were determined in excavations, with the help of dendrochronology. These phases date from between 737 AD and 968 AD.
Danevirke has a length of about 30 km total, and measures between 12 and 20 feet in height. During the middle ages, the structure was enforced with palisades and walls, and used by Danish kings as a gathering point for Danish military excursions and crusades, particularly the Danish raids against the Slavs. In the 12th century, King Valdemar I "the Great" reinforced parts of Danevirke with a brick wall, which underlines the continued strategical and military importance of the structure, throughout the middle ages.
Danevirke was last used as a means of Danish defense in the Danish-Prussian war of 1864, without much luck, however. Badly maintained during that war, Danevirke was given up as a means of defense by Danish governments after its capture by the Austrians and Prussians, and the following Prussian occupation of Schleswig and Southern Jutland ("Slesvig" or "Sønderjylland" in Danish).
During World War II the Germans integrated Danevirke as a means of defense against the feared allied invasion from the North Sea, in which the structure would bolster German defenses in case of an Allied conquest of Jutland.
- Aerial photo of the Danish "Dannevirke" (http://www.gimpster.com/danish/kongemagt/image_viewer.php?section=dannevirke&name=luftfoto)