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Breakthrough in Dating Viking Fortress

In 2014, archaeologists from the Museum of South East Denmark and Aarhus University discovered the previously unknown Viking fortess at Borgring south of Copenhagen. Since then, a search has been taking place to uncover the life, function, destruction and, not least, the precise dating of the Viking fortress. Now, a new find has resulted in a breakthrough in the investigation.

2017.07.04 | Arts Kommunikation

The Borgring fortress had four gateways, oriented towards the principal points of the compass. The North Gateway, which was destroyed in a violent conflagration, is currently being excavated (Photo: The Museum of South East Denmark / bo47nielsen).

The carved oak timber object recently found in peat layers just outside the south gateway of the fortress. The piece has been cut and sampled for dendrochronological sampling (left). The function of the piece is unknown, but it may be a part of a door or building (Photo: The Museum of South East Denmark / Nanna Holm).

In the period 2016–18, a programme of new excavations is made possible by a grant from the A.P. Møller Foundation. The team from the Museum of South East Denmark and Aarhus University are joined by leading experts from the Environmental Archaeology and Materials Research at the National Museum of Denmark and the National Police Department's Section for arson investigation. Prior to this year’s excavations, we only knew that the massive, 150m-wide fortress dated to the tenth century. Experts suspected that it was built in the reign of Viking king Harald Bluetooth (c. 958–c.987), but the association could not be established with certainty.

A 1000 years old plank
On Monday 26 June, the archaeological team opened new trenches is the meadow next to the fortress to search for evidence of the landscape surrounding the fortress. Around 2.5 meters below the current surface of the valley, a c. 1m-long piece of carved oak wood was found, with drilled holes and several wooden pegs in situ. The wood carries clear traces of wear, but it is not currently possible to ascertain the function of the wood piece.

Leading specialist in dendrochronological dating, Associate Professor Aoife Daly from the University of Copenhagen and owner of dendro.dk, has just completed his study of the piece of wood and says: "The plank is oak, and the conserved part of the tree trunk has grown in the years 829–950 in the Danish area. A comparison with the material from the Trelleborg fortress in Sjælland shows a high statistical correlation, which confirms the dating. Since no splints have been preserved, the tree has fallen at some point after year 966 ".

Corresponding with other ring fortresses
Research leader Jens Ulriksen says: "The wood piece was found on top of a peat layer and is fully preserved, as it is completely water-logged. We now have a date of the wood in the valley of Borgring, which corresponds to the dating from the other ring fortresses from Harald Bluetooth’s reign. With the dendrochronological dating, in conjunction with the traces of wear the piece exhibits, it is likely that the piece ended as waste in the late 900s, possibly in the early 1000s."

"In the coming week, the National Museum of Denmark's environmental archaeologists will take samples of wet depositions in the valley with the aim of uncovering how the layers have evolved from the earliest strata we have dated to the Bronze Age and over time," says excavation leader Nanna Holm. Nanna Holm, of course, hopes that the studies will particularly clarify one of the unclear questions archaeologists have, namely where the river was exactly when the fortress was built in the Viking Age, and how passable it was.

Søren M. Sindbæk, professor in Archaeology at Aarhus University and part of the excavation team, says: “This find is the major breakthrough we have been searching for. We finally have the dating evidence at hand to prove that this is a late tenth-century fortress. The exact year is still unknown, but since the find also shows us where the river flowed in the Viking Age, we know where to look for more timber from the fortress.”

For questions about the project, please contact:

  • Excavation leader Nanna Holm (tel. +45 3119 0648)
  • Professor in Archaeology Søren M. Sindbæk (tel. +45 2280 6539, farksms@cas.au.dk)
  • Dendrochronologist Specialist, Associate Professor Aoife Daly (tel. +45 2625 4108)