In what's been called a "sensational" find, archaeologists have discovered a Viking fortress near the Danish city of Køge, about 30 miles southwest of Copenhagen. The ancient ringed structure is said to have a diameter of 475 feet and to date back more than 1,000 years.

“This is the first time for more than 60 years that a new Viking ringed fortress has been discovered in Denmark,” Nanna Holm, curator of the Danish Castle Center and one of the archaeologists involved in uncovering the ruin, said in a written statement issued by Aarhus University.

Lasse Sonne, a University of Copenhagen historian who specializes in the Viking period, called the discovery “great news.”