Ancient fingerprint found on 2,400-year-old Danish war boat

The Hjortspring boat was discovered on the Danish island of Als and first excavated in the early 1900s. Archaeologists believe it was used by a band of warriors who launched an attack on the island but were ultimately defeated. Although the weapons found with the vessel were typical of the time and widely used across Northern Europe, researchers have long struggled to pinpoint exactly where these warriors originated or when they built the boat.

Carbon Dating and Chemical Analysis of Ancient Caulking

To answer those questions, the research team examined previously unstudied materials recovered with the vessel, including cordage and waterproofing caulk. They used radiocarbon dating to determine age and applied gas chromatography -- mass spectrometry to identify the caulking's chemical makeup. Their analysis showed that the waterproofing material was made from animal fat mixed with pine pitch.

During the first millennium BCE, pine forests were scarce in Denmark. While it is possible that pine pitch was obtained through trade, extensive pine forests did grow along parts of the Baltic Sea coast east of Denmark. This evidence suggests the boat may have been constructed in one of those eastern regions. If that is correct, the vessel and its crew likely crossed a significant stretch of open sea to reach Als, pointing to a carefully planned and organized military expedition.

Radiocarbon testing of the cordage and caulk indicates the boat was built between the 4th and 3rd centuries BCE. That timeframe aligns with earlier dating of wooden remains from the Hjortspring site.

A Rare Fingerprint From the Iron Age

One of the most striking discoveries was a partial human fingerprint preserved in the caulking. Although researchers cannot determine exactly who left it, they believe it may have been pressed into the tar during a repair by a crew member. As the team explained, the mark may be "providing a direct link to the seafarers of the ancient vessel."

The authors note: "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."

They added, "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."

Solving a Century-Old Scandinavian Mystery

According to the researchers, "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 researchers also explained why dating the boat has been challenging. "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 funded by the Marcus and Amalia Wallenberg Foundation grant awarded to M.F. for Complex Canoes project (grant number: 2022.0108) and the 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.