Researchers at Lund University in Sweden identified a fingerprint preserved in tar that sealed Scandinavia's oldest plank-built boat, providing a rare physical connection to the warriors who used the vessel more than 2,000 years ago.
During the fourth century BCE, a small fleet of boats launched an attack on the island of Als off the coast of present-day Denmark. The raiders, who may have sailed on four boats, were ultimately defeated. After the battle, the defenders placed their enemies' weapons in a bog along with one of the boats, apparently as a ritual offering to mark their victory.
"Where these sea raiders came from, and why they attacked the island, has long been a mystery," said Mikael Faubel, an archaeologist at Lund University.
The boat was first discovered in the 1880s in the Hjortspring Mose bog, excavated more extensively in the 1920s, and has since been known as the Hjortspring boat. It remains the only prehistoric plank-built boat ever found in Scandinavia and has been on display at the National Museum of Denmark ever since.
When researchers recently located fragments of the boat that had never undergone chemical preservation, they were able to analyze them using modern scientific techniques. "We discovered the boat was sealed with pine tar, which was surprising. This suggests the boat was built in a location with extensive pine forests," Faubel said.
Previous theories suggested the boat and its crew came from Hamburg in present-day Germany, but the new evidence points instead to origins in the Baltic Sea region.
The latest findings result from meticulous detective work by the researchers. The team wanted to find material from the boat that had not yet been preserved. This included examining archives at the National Museum and reading old correspondence detailing when and where materials were sent between different storage areas and museums in Denmark.
"When we located some of the boxes containing the materials, we were very excited to discover they contained samples from the original excavation that had not been studied for over 100 years," Faubel said.
The researchers used a wide range of modern scientific methods to study the material they found. They succeeded in performing carbon dating on some of the lime bark ropes used in the boat, which gave them the first absolute date from the original excavation material and confirmed its dating to the Pre-Roman Iron Age.
They also used X-ray tomography to perform high-resolution scans of the sealing material and ropes found on the boat. This included creating a three-dimensional digital model of the fingerprint found in part of the sealing tar.
They used gas chromatography and mass spectrometry to investigate the sealing material and see how it was produced. Additionally, they worked with modern rope experts to create replicas of the ship's ropes to study the rope-making process used in the boat's construction.
"If the boat came from the pine-forest-rich coastal areas of the Baltic Sea, this means the warriors who attacked the island of Als chose to launch a maritime raid across hundreds of kilometers of open sea," Faubel said. "We also hope to be able to extract ancient DNA from the sealing tar on the boat, which could give us more detailed information about the ancient people who used this boat," Faubel concluded.
