In the narrow part of Jutland the Danish king built a fortress of mighty oak and earth. The fortress consisted of several ramparts. The first was built in 737 and the last one at the end of the 1100’s.
This bulwark, the Dannevirke, was built in the age of the Vikings to protect Denmark from the powerful Frankish kings just to the south.
An old chronicle, The Chronicle of the Lejre Kings, tells that the Danes stood up to anyone that attacked them. Jutland was most exposed to attack and was therefore covered by a bulwark of wooden stakes.