Hundreds of years before the Viking Age, Nordic Bronze Age societies were likely proficient open-sea navigators who regularly crossed large tracts of ocean directly between what is now Denmark and Norway, suggest a new study published in PLOS ONE. Led by Boel Bengtsson of the University of Gothenburg and colleagues, the work helps clarify the sea-going abilities of Bronze Age peoples and contradicts the longstanding views of many experts who presumed Bronze Age societies only traveled along coastlines.

Sea trials in a reconstruction of the c. 350 BCE Hjortspring boat, akin to a Scandinavian Bronze Age type boat, with a side view drawing of the boat under full crew inserted above. PH๏τo by Knut Valbjørn. Credit: Boel Bengtsson, CC-BY 4.0

Using a state-of-the-art computer simulation tool known as the “Voyage Optimization Tool,” the scientists combined archaeological data, simulated boat performance, and environmental modeling to test the feasibility of two sea routes: a longer coastal route of approximately 700 kilometers and a direct open-sea route of approximately 110 kilometers across the Skagerrak Strait. They sought to determine whether the people of the Bronze Age had the technical ability and navigational skills to travel long distances across the sea out of sight of land.

Central to the investigation was the use of performance data from experimental replicas of Bronze Age sewn-plank boats such as the Hjortspring and Ullerslev. These vessels, driven by paddle and constructed from planks sewn together with natural fibers, were ᴀssessed in various wind, wave height, and crew workload conditions. The simulations showed that in fine summer weather—with waves below a meter in height and winds below 10 knots—open-sea crossings were not only possible but considerably faster, cutting travel time by up to 25% compared with the safer but much longer coastal route.

“Regular open-sea crossings of the Skagerrak, including some 50 km of no visible land, likely commenced by 2300 BC, as indicated by archaeological evidence,” according to the researchers. These trips would have required not only seaworthy boats but experienced crews with detailed knowledge of maritime conditions. The researchers theorize that seafarers probably relied on techniques like solar orientation, landmark tracking, and possibly even animal behavior to guide their navigation—methods still used in some indigenous maritime cultures today.

A comparison between the Hjortspring boat and southern Scandinavian boat depictions. PH๏τo of the Hjortspring boat taken by Boel Bengtsson. Credit: B. Bengtsson et al. PLoS ONE (2025) / CC BY 4.0

While the coastal route was safer and offered the chance to restock supplies, it also posed logistical challenges that may have made it impractical for time-sensitive or priority travel.

The study not only adds to our understanding of Bronze Age maritime culture but also provides a powerful methodological tool for future research. The modeling system can be adapted for use with other modern and ancient vessels, providing researchers with a dynamic way of hypothesis-testing prehistoric seafaring across the globe. By combining decades of archaeological research with cutting-edge simulation technology, this study ushers maritime archaeology into a new era of evidence-based exploration.

Cumulus clouds forming over northern Denmark, as viewed from Lilla Pölsan (4 km due west of the islands of Rörö/Hönö) in the northern Gothenburg archipelago with the light house on Stora Pölsan in the foreground. Credit: Boel Bengtsson

Apart from navigation, the findings also help to explain archaeological patterns observed across the Nordic region. The similarities in artifacts, burial practices, and architecture between northern Denmark and southwest Norway are indicative of frequent contact and exchange. Researchers argue that the similarities are a result of regular open-sea voyages, and not just coastal hopping as previously ᴀssumed.

More information: Bengtsson B, Montenegro A, Green A, Tomasini M, Prince M, Skärström VW, et al. (2025) Seafaring and navigation in the Nordic Bronze Age: The application of an ocean voyage tool and boat performance data for comparing direct open water crossings with sheltered coastal routes. PLoS ONE 20(4): e0320791. doi:10.1371/journal.pone.0320791