Danish archeologists have uncovered a technologically advanced fortress from the late 10th century—the first one discovered in more than six decades.
Located south of Copenhagen on the island of Zealand and known as Borgring, this perfect circle fortress was discovered by using a high-resolution LiDAR mapping (an aerial, laser-based surveillance) that produced a 3D topographical ground map. While excavations began in 2014, the first comprehensive report was published earlier this month in Antiquity.
Researcher Soren Michael Sindbaek, an archaeologist at Denmark’s Aarhaus University and a corresponding author of the study, has been searching for evidence of Viking fortresses for some time now. He explained to Science that he selected locations based on “landscape features that matched fortresses we knew already, namely accessibility to land and water routes.” There were gaps in the maps of Denmark where he believed fortresses should have been, which is precisely where he found Borgring.
The first Viking fortresses of this type were discovered in Denmark in the 1930s. This is the fifth ring-shaped fortress, known as trelleborgs, to have been found. They were inspired by English designs, as some Viking techniques were influenced following the Norse conquest. Designs for military forts of this kind were standardized, with four perpendicular entrances, two intersecting streets in the center and several shared households. They measured 130-200 meters in diameter and were protected by a ditch, wooden fence and defensive wall.
The ring was considered an ideal shape for a fortress—it encompassed the largest area with the smallest circumference. There was no need to create a perfect circle fortress, but Borgring was. With the Vikings combining land-surveying skills and strict geometry to construct a prestigious structure, Sindbaek to believes this fortress not only served a military purpose, but was intended to celebrate the power of the King who ordered it.
What makes this fortress so different? Scientists have found carpentry instruments and other tools used by the Vikings to patch holes in their defensive walls and fences. They also concluded that Borgring was inhabited by many generations, an anomaly as other forts were normally abandoned one or two decades after construction.
Since its discovery, there’s been a lot of debate about who would have built such a unique structure. But archaeologists believe they may have found the answer—thanks to a stump of wood discovered in July of this year. By using both a Northern European database of oak samples and by comparing the stump with four other Viking ring fortresses at Trelleborg, the team concluded that the wood came from a tree in Denmark that was cut down after the year 966. That would place it squarely in the reign of Harald Bluetooth, the son of the first ruler of the Danish kingdom and the person who introduced Christianity to his people during his reign from 958 to 986.
Sindbaek and his team believe there may be more fortresses hidden in the Danish countryside, and the hunt is on to find them.