A Viking 'ring fortress' at Trelleborg in western Zealand
It's been long thought that Denmark is the home to four Viking ring fortresses, but the first discovery in 60 years may shed new light on the Viking Era and King Harald Bluetooth.

“This is big news! We share the Viking era with other countries, but these ring fortresses are unique to Denmark and many had given up hope that there were more remaining,” Viking Age historian Lasse Sonne from the University of Copenhagen’s Saxo Institute told Politiken.
Archaeologists have thus far uncovered just small portions of the new fortress, which is being dubbed Vallø Borgring. Researchers have not yet definitively dated the fortress, but think that, like the previously-discovered ring fortresses – Aggersborg and Fyrkat in northern Jutland, Trelleborg in western Zealand and Nonnebakken near Odense – it likely dates back to over a thousand years ago when Harald Bluetooth ruled as king from 958 until his death in 985 or 986.