What is the Danevirke? Over 1000 years ago in the Viking Age, Danes, Frisians, Saxons and Slavs came into contact in this border region between Scandinavia and Central Europe. Danish kings began to fortify the Danevirke to secure the southern frontier of their kingdom and protect the trade route between the North Sea and the Baltic. The Danevirke consisted of earthworks, walls, ditches and an offshore defensive structure in the Schlei. The most important trading centre and transport hub was Hedeby.