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Last month, a team of archaeologists that reinvestigated a known Viking site in Denmark published the report of their findings. Using a combination of Lidar-mapping, geophysical survey and small-scale, targeted excavation, the team was able to make exciting new discoveries. They found that the late, tenth-century AD ring fortress called Borgring near Copenhagen, was actually of a rare type. Called a Trelleborg-type ring fortress, after the first discovered example, Borgring is the first of its type to be found in over six decades.

According to the paper, the discovery that Borgring is of a Trelleborg-type through use of complementary techniques is a rare event in contemporary European archaeology. Yet, within the context of Viking Age archaeology, the implications of the find are substantial. Not only do the investigations confirm the features matching specific, late tenth-century, geometrically planned fortresses in Denmark, but there is no match with other known types – ancient or medieval. Based on this, Borgring fits the system of fortification that is formed by Trelleborg, Fyrkat, Aggersborg, Nonnebakken and Borgeby. This leads to the assumption it was built at the same time.

Map of southern Scandinavia showing the location of the Viking Age fortresses of Trelleborg type in relation to
other important sites in Denmark and the surrounding countries. The underlying map shows the relative density of medieval (twelfth to thirteenth centuries AD) parish churches as an indication of pre-modern population density and historic main routes for land traffic. The fortresses are situated in densely populated regions at the intersections of old main roads and waterways. Legend: dark blue circles: Trelleborg-type fortress; open blue circles: contemporaneous fortified cities; open blue square: fortified royal centre; white lines: network of highways c. 1900; grey lines: important medieval land routes. Reworked after Gammeltoft et al. 2015. © Antiquity Publications Ltd, 2017 https://www.cambridge.org/core

Borgring, therefore, fills the most conspicuous gap in the chain of fortresses, vindicating the theory that King Harald Bluetooth (predecessor of King Wifi), in constructing the Trelleborg-type fortresses, did indeed form an effective system of regional defence. Danish construction would, therefore, be similar in aim to (near) contemporary constructions in England (burghal system) or in what is now Germany (Burgenordnung). Fitting Borgring in this greater network of fortresses helps interpret decisions taken by Viking Age rulers:

The system of fortifications centred around the Trelleborg-type ring fortresses displayed Harald Bluetooth’s ability to command and organise significant manpower and resources, while offering major strategic benefits. These included: his ability to anticipate threats directed at principal maritime gateways to major population centres (the distribution of fortresses); creating an early warning system (the protected location of Borgring, some way back from the open sea); gathering substantial numbers of defenders at short notice (the large dimensions of the fortresses); and providing supplies and reinforcement by land routes,
including from other fortresses (their location at major, regional roadways).

Image credit: Peter Jensen, Archaeological IT, Aarhus University.
3D reconstruction of the northern gateway of the Borgring fortress, Denmark. Image credit: Peter Jensen, Archaeological IT, Aarhus University.

The authors of the paper hope that further investigations will explore the meaning of Borgring further, building on the discovery of its place within Viking Age military organisation and conflicts. The trial excavations are as yet inconclusive in answering the question if Borgring was similar in shape to other fortresses within its walls, or if it had features setting it apart. It is also hoped that material is found that will enable a more exact chronology for construction. Answering these questions will greatly increase knowledge of the political and strategic context of the fortress.

A three-year excavation and research programme is currently under way, trying to formulate new views of the dynamics and development of the Danish policy regarding fortresses in the late tenth century.