A new analysis of the Hjortspring boat, an ancient wooden plank boat now on display in the National Museum of Denmark, has yielded clues to its potential origin — which has long been considered a mystery, according to a study published December 10, 2025 in the open-access journal PLOS One by Mikael Fauvelle from Lund University, Sweden, and colleagues.
The ancient Hjortspring boat was discovered on the Danish island of Als and first excavated in the early 20th century. Researchers believe it belonged to a group of warriors who attacked the island and were defeated, but archaeologists have not previously determined precisely where these warriors came from and when.
For this paper, the researchers carbon-dated and analyzed some previously unstudied caulking and cord materials found with the boat. Using gas chromatography - mass spectrometry, they determined that the caulk was likely made up of animal fat and pine pitch.
At this point in history, Denmark itself had few pine forests. The researchers note that it is possible that pine pitch somehow reached Denmark via trade. However, other coastal areas along the Baltic Sea, east of Denmark, did have pine forests, leading the researchers to believe that the boat may have been built in these regions, and it and its warriors may have come from this direction. If true, the boat would likely have traveled a long distance over the open ocean to reach Als, potentially indicating a notably organized and premeditated attack.
Carbon-dating of the cords and caulk found that the boat was likely built somewhere in the 4th or 3rd century BCE, which lines up with previous datings of wood from the Hjortspring site.
In addition, the team found a partial human fingerprint in part of the caulking material during their study. While they were unable to determine exactly where this fingerprint may have come from, the researchers suggest that it could have been left by one of the crew members during a repair of the boat, "providing a direct link to the seafarers of the ancient vessel."
The authors add: "New analysis of Scandinavia's oldest plank boat brings us a step closer to solving the 100-year-old mystery of the ancient boat's origins. Using cutting-edge scientific methods, researchers have zeroed in on the Baltic Sea Region as the most likely source for the circa 2,400-year-old boat, while also discovering a fingerprint left by an ancient seafarer in the tar used to waterproof the vessel."
"Finding a fingerprint on the tar fragments from the boat was a big surprise for us. Fingerprints like this one are extremely unusual for this time period. It is great to have found a direct connection with one of the people who used this ancient boat."
"The boat was used by a small army of invaders who attacked the island of Als in southern Denmark over 2,000 years ago. The invaders were defeated and the local defenders sunk the boat into a bog as an offering to give thanks for their victory. Ever since the boat was excavated from the bog in the early 1920s, the question of where the invaders came from has been an open mystery. The weapons they used which were found in the boat were quite common for the time and were used throughout Northern Europe, giving us few instructions as to their origins. Several different theories for the boat's origins have been proposed over the past 100 years, with some scholars suggesting the boat's crew came from somewhere in northern Germany or perhaps a different part of modern-day Denmark. Now our scientific analysis of the boat's caulking material gives us the first major new clue in over a century. The boat was waterproofed with pitch from pine trees, which were rare in both Denmark and northern Germany during the first millennium BCE. We argue that this means the boat and its crew most likely came from further east along the shores of the Baltic Sea where pine forests were more abundant."
"The boat was excavated before modern dating methods were available and most of the material from the boat was immediately conserved using chemicals that make radiocarbon dating impossible. Going through the archives, however, we were able to find some original cordage that had not been conserved. We obtained a radiocarbon date from the cordage that returned a date range of between 381 and 161 BCE, confirming the pre-Roman Iron Age date of the boat."
In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/44sjLHv
Video caption: Archaeologist Mikael Fauvelle talks about the findings at the National Museum of Denmark, where the Hjortspring boat is on display.
Video credit: Lund University, CC-BY 4.0 ( https://creativecommons.org/licenses/by/4.0/ )
Video link: https://plos.io/4p8Dt3f
Citation: Fauvelle M, Bengtsson B, Pipping O, Hollmann M, Mortensen MN, Toft P, et al. (2025) New investigations of the Hjortspring boat: Dating and analysis of the cordage and caulking materials used in a pre-Roman iron age plank boat. PLoS One 20(12): e0336965. https://doi.org/10.1371/journal.pone.0336965
Author countries: Sweden, Denmark
Funding: This research was supported by grants from the following funders: Marcus and Amalia Wallenberg Foundation grant awarded to M.F. for Complex Canoes project (grant number: 2022.0108) Riksbankens Jubileumsfond grant awarded to J.L. for Maritime Encounters program (grant number: M21-0018). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
