Aggersborg is Denmark's largest Viking castle. It is located in Nordjylland on Aggersund north of the Limfjord and was archaeologically explored between 1945 and 1948.
The castle complex has an inner diameter of 240 meters and an outer diameter of 288 meters. There is a flat area of 8 meters between the wall and the ditch. The ditch was about 1.30 meters deep, the wall about 4 meters high.