Tiny fingerprint can solve 2,000-year-old mystery of who attacked a Danish island

Scientists might be close to solving a long-standing mystery of why the Danish island of Als was attacked over 2,000 years ago. They have found a fingerprint which could reveal the identity of the seaborne raiders. This mark, possibly left behind by the culprits, was discovered on Scandinavia’s oldest plank boat and was pressed into the tar caulking material. Known as the Hjortspring boat, it was first discovered in the 1880s and excavated in the 1920s. It was one of the four ships that were likely used by the raiders in the fourth-century BCE attack. The island dwellers defended themselves and managed to sink one of them. However, even after all these years, who these people were and their motive for attacking Als remains a mystery. “Where these sea raiders might have come from, and why they attacked the island of Als has long been a mystery,” Mikael Fauvelle, an archaeologist from Lund University, said in a statement in 2025.

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Ship's origin traced to the Baltic Sea region

The researchers used modern tools to study the portions of the ship that were not chemically preserved. They found that pine pitch was used for waterproofing, which suggests "the boat was built somewhere with abundant pine forests." This changed one theory about the origin of the ship, as earlier, they believed that the raiders likely originated from modern-day Hamburg, Germany. However, they now think that they came from the Baltic Sea region, since this portion, which lies east of Rugen and Scania, is abundant with pine forests. Fauvelle said that if this were the case, then it means that the warriors "launched a maritime raid over hundreds of kilometres of open sea."

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Ancient DNA from ship can reveal the invaders

Carbon dating of the lime bast cordage confirmed that the ship came from the pre-Roman Iron Age. They then used X-ray tomography to take high-resolution scans and created a 3D model of the fingerprint. They also employed chromatography and mass spectrometry to help see how the caulking tar was produced, Popular Mechanics reported. The team is now trying to extract ancient DNA from the caulking tar on the boat to understand the origins of these people. The authors further wrote that the analysis sheds light on the methods and materials used to build Scandinavia’s first plank boats. It also shows how little we know about the early maritime societies in Northern Europe.