In the 4th century BCE, at least four wooden plank boats the island of Als off the coast of Denmark. The unknown attackers were defeated, with the defenders sinking the weapons of their foes into the bog in one of these boats, known as the Hjortspring boat, most likely to give thanks for their victory. Archaeologists have now carbon-dated and analyzed caulking and cord materials found with the boat and also discovered a partial human fingerprint found on a fragment of caulking material. This remarkable fingerprint provides a direct link to the ancient seafarers who used the Hjortspring boat.
Photo of caulking fragment showing fingerprint on the left and high-resolution X-ray tomography scan of fingerprint region on the right. Image credit: Erik Johansson / Sahel Ganji.
The Hjortspring boat was discovered in 1880s during peat digging in the Hjortspring bog on the island of Als off the southeastern corner of Jutland, Denmark.
Formal investigations of the bog and boat find started in 1920 following the reunification of southern Jutland with Denmark.
The boat was excavated by Gustav Rosenberg between 1921 and 1922 and about 40% of the original boat was recovered from the bog, allowing for a full reconstruction of the boats form.
Enough iron spearpoints and shields to outfit a military band of around 80 warriors were deposited together with the boat — far more individuals than could have fit inside the boat itself.
Based on these finds it has been suggested that a band from an unknown location traveling in up to four Hjortspring style boats attacked the island of Als and was defeated, with the victors depositing the weapons of their vanquished foes together with one of their boats into the bog to give thanks for the victory.
After excavation the boat was conserved and has been on display in the National Museum of Denmark since 1937.
In the new study, Lund University archaeologist Mikael Fauvelle and his colleagues 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.
“It is possible that pine pitch somehow reached Denmark via trade,” the researchers said.
“However, other coastal areas along the Baltic Sea, east of Denmark, did have pine forests, leading us 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.”
The Hjortspring boat as currently displayed at the National Museum of Denmark. Image credit: Boel Bengtsson.
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 scientists found a partial human fingerprint in part of the caulking material during the study.
While they were unable to determine exactly where this fingerprint may have come from, 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.
“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,” they said.
“Using cutting-edge scientific methods, we 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.”
The study was published online in the journal PLoS ONE.
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M. Fauvelle 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; doi: 10.1371/journal.pone.0336965
