The fortress found on the Danish island of Zealand, around 30 miles south of Copenhagen, is the fifth circular fortress to be unearthed, and the first in over 60 years. “This is great news,” said Lasse Sonne, a Viking historian from the Saxo Institute at the University of Copenhagen. “Although there were Vikings in other countries, these circular fortresses are unique to Denmark. Many have given up hope that there were many of them left.” Like previously discovered ring fortresses, the Vallø Borgring is thought to date back to the late tenth century and the reign of Harald Bluetooth, the...