New Research

The Mysterious Hjortspring Boat That Sank in Denmark 2,400 Years Ago Is Still Revealing Its Secrets

New research suggests indicates that Scandinavia’s oldest known example of a wooden plank boat may have sailed to attack the island of Als from the east, indicating a planned effort

Sonja Anderson | Daily Correspondent

December 23, 2025

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Around 2,400 years ago, a group of seafaring warriors attacked the island of Als, located off the coast of modern-day Denmark. The islanders successfully defended Als, and they ceremoniously sank their attackers’ boat in the Hjortspring bog.

In the 1920s, researchers excavated the vessel’s remains, and the fragments went on display at the National Museum of Denmark. Known as the Hjortspring boat, it’s Scandinavia’s oldest known wooden plank boat, but its origins have been a mystery since its discovery.

Now, researchers have discovered important clues about the vessel’s story. According to a study published this month in the journal PLOS One, the boat was made between the fourth and third centuries B.C.E., during the Iron Age. Researchers think it came from east of Als.

“This means that the crew of the boat traveled hundreds of kilometers by sea to launch their attack on Als in southern Denmark,” lead author Mikael Fauvelle, an archaeologist at Lund University in Sweden, tells Discover magazine’s Anastasia Scott. “While we will never know exactly what drove around 80 warriors to attack Als some 2,400 years ago, these findings suggest it was an inter-regional conflict that involved substantial planning and logistical capacities.”

The Hjortspring boat was nearly 66 feet long, and it could hold 24 men with their weapons and gear. According to the study, however, the trove of iron spearpoints and shields found with the boat would have been enough for 80 warriors. As such, researchers think four Hjortspring-style boats may have attacked Als, and the victors included all the attackers’ weapons with the vessel that they sank “to give thanks for the victory.”

“Because the Hjortspring boat was purposefully sunk in a bog as an offering, it was preserved in the unique low-oxygen environment for over [2,000] years, making it the only preserved example of one of these boats that we have,” Fauvelle tells Discover.

The researchers determined the vessel’s age by radiocarbon dating its lime bast cordage—rope made from the bark of lime trees. They also used gas chromatography and mass spectrometry to analyze its caulking, the sealant used to make it waterproof.

“The boat was waterproofed with pine pitch, which was surprising,” Fauvelle says in a statement from Lund University. The caulk was made of dried pine sap and animal fat. “This suggests the boat was built somewhere with abundant pine forests.”

At the time the Hjortspring boat was made, Denmark’s main peninsula had few pine forests, per the study. However, some areas bordering the Baltic Sea had an abundance of pine. Researchers think the boat may have come from a place like northern Poland, the Danish island of Bornholm, or Sweden’s Blekinge or Gotland.

Since the seafarers made such a long journey to Als, their attack was likely “premeditated and planned, possibly as part of a pan-regional political or military dispute,” write the study authors.

The research “shows that the Scandinavian seafaring tradition of raiding and trading, most famously associated with the Viking Age, has very deep roots that go back thousands of years to the early Iron and Bronze Ages,” Fauvelle explains to CNN’s Taylor Nicioli. “It also shows that ancient Scandinavia was a very interconnected region. Much like today, political conflicts and alliances transcended regional boundaries, and people must have had … [contact] with each other over considerable distances.”

Ancient seafaring expert Ole Kastholm, a researcher at the Roskilde Museum in Denmark, praises the new study. Based on the new evidence, it’s possible that the Hjortspring boat may have traveled from the Baltic region, he tells CNN.

Fingerprint of ancient seafarer found on Scandinavia's oldest plank boat

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“We have a modern tendency to underestimate the people of the past and their achievements—but they actually rowed and paddled in small, open vessels across the North Sea, Skagerrak and the Baltic Sea,” Kastholm adds.
“This could have been in logboats, and in smaller plank-built boats such as the Hjortspring boat.”

While conducting their research, the study authors spotted an extremely rare mark on some caulking material from the Hjortspring boat: a human fingerprint. “Fingerprints are very rare for this time period and area,” Fauvelle adds. “To find one on such a unique boat is extremely special.”

After the Hjortspring boat was excavated, it was reconstructed at the National Museum of Denmark. During this process, preservatives were applied to its wooden planks. Later, when radiocarbon dating became available, researchers were unable to date the wood due to the added chemicals. Fortunately, researchers were able to use intact cordage to perform radiocarbon dating.

“The study also shows how important it is that we in our museum collections take care of old artifacts,” study co-author Flemming Kaul, a researcher and curator at the National Museum, tells CNN. “When the Hjortspring boat was excavated in 1921, one could not have known that 100 years later there would be a number of highly specialized methods that would be able to extract knowledge from even the most insignificant pieces from the excavation. Hopefully one day we are able to pin down the exact geographical origin of this unique vessel.”

Sonja Anderson | Read More

Sonja Anderson is a writer and reporter based in Chicago.