During excavations of the Viking-age ring fortress Borgring, Denmark, traces of a devastating fire was uncovered. The National Forensic Services of the Danish Police were invited to participate in a novel collaboration, applying contemporary forensic fire investigation to an archaeological site. This paper presents the results and sets a benchmark for future applications. The investigation leads to a revised reconstruction of the fortress and the development of the fire. The application of fire investigation methods, following the Daubert standard criteria, enhance the documentation and analysis of archaeological sites, while archaeological methods show significant potential at modern fire scenes.

Viking Age ring fortresses were some of the largest construction projects in Danish prehistory. In this article we reconstruct the amount of turf and timber used in the construction of the Borgring ring fortress and estimate the resource area needed to supply the building materials. Using REVEALS pollen data modelling, we quantify the regional oak land cover and estimate the resource area. The results show that even though Borgring was built in an open cultural landscape, sufficient supply of oak for the construction would have been accessible within a few kilometres from the fortress.

In 2014, Borgring, near Køge, Denmark, was identified as the fifth geometrical Viking Age ring fortress in Denmark, complementing an exclusive group of monuments including Trelleborg. Excavations and surveys in 2016–18 allow a detailed reconstruction of the site and its history. Borgring is a fortification with the same geometry, construction, and location as other Trelleborg-type fortresses, though exhibiting notable differences. Finds, including beads, ornaments, and iron tools, reflect activities and links to other fortress sites. The dating of Borgring is established with reference to wiggle-matched 14C dates.