Aggersborg is the largest of Denmark's former Viking ring castles, and one of the largest archeological sites in Denmark. It is located near Aggersund on the north side of the Limfjord. It consisted of a circular rampart surrounded by a ditch. Four main roads arranged in a cross connected the castle centre with the outer ring. The roads were tunnelled under the outer rampart, leaving the circular structure intact. The modern Aggersborg is a reconstruction created in the 1990s. It is lower than the original fortress.