Trelleborg in Denmark is one of five known ring fortresses constructed at the same time. While similar in layout and style, Trelleborg remains the best preserved and was the only fortress with a fortified outer wall. These fortresses must have taken a lot of manpower and time to build, but there is no contemporary information preserved in literature about them.
Trelleborg and Harald Bluetooth
Wood used in the construction of the outer rampart has been dated to about 980 A.D., which was about the time of Harald Bluetooth’s reign. They were only occupied for a little over a decade. It is probable that they were abandoned after the death of Bluetooth during a civil war against his son Sven Forkbeard because the fortifications were expensive to maintain.
The Fortress’ Purpose
The reasons for the construction of these fortresses are unknown. However, the theories include to defend Bluetooth’s territories, to serve as staging areas for invading neighboring areas, and to suppress the local population. One suggested meaning of Trelleborg is “slaves of the fortress,” which may have been meant as an insult to the petty kings and other tribal leaders of the time. However, there is some debate as to whether the Vikings called this fortress “Trelleborg” when they occupied it.
Outer Layout
Trelleborg consists of an outer ward and an inner fortress. The outer ward had 15 longhouses built side by side and radiating toward the outer rampart. Two of the longhouses are isolated; it is unclear why. The moat around the outer rampart contained water. There is some evidence suggesting that the outer rampart of the fortress may not have been completed.
A timber bridge stood midway between the two main gates in the southeast area of the fortress. This required invading forces to travel a long way to get from one gate to another and would expose the invaders to continuous enemy fire.
Trelleborg’s Inner Layout
The inner fortress is 136 meters (about 148 yards) in diameter with inner rampart being 17 meters (about 18 yards) wide and five (about 5 yards) meters high. The inner fortress was surrounded by a moat. However, there is no evidence that the moat had water. Wood remnants found in the moat may have been spiked stakes or planking. The inner rampart had four gates at the cardinal points of the compass, with that part of the fortress following a cruciform plan. Each of the four quadrants contained four “high-end” longhouses that shared an “exactly surveyed” courtyard.
Modern History of the Fortification
In 1933, a motorbike club rented the site with plans to turn it into a motocross track. However, the excavation of the site took over nine years, and those plans were abandoned. The other four ring fortresses are Borgring, Nonnebakken, Fyrkat, and Aggersborg. In September 2023, UNESCO added the Viking-era sites to the World Heritage List. After the announcement of the listing, Trelleborg experienced a 65 percent increase in tourist visits.
Sources: Children of Ash and Elm by Neil Price (2020).
