The fingerprint of one of seafarers who built the oldest known wooden plank boat in Scandinavia has been discovered in the tar used to waterproof it. A new study of caulking and cordage fragments revealed the presence of the fingerprint and provided new evidence on the boats possible origins and the techniques used to make it.First discovered by peat diggers in the Hjortspring bog on the island of Als off Jutland, Denmark, in the 1880s, it was fully excavated in 1921 and 1922. About 40% of the boat was recovered, enough to allow a full reconstruction of its form. The boat was about 20 meters (66 feet) long, weighed 530 kilos (1,170 pounds), and could carry 24 people plus gear. It was built from lime wood planks sewn together with cordage.A large number of spearpoints and shields were deposited in the bog with it, enough to outfit about 80 warriors. Archaeologists believe raiders in up to four similar-sized boats attacked Als but were defeated. The islanders then deposited the boat and the raiders weapons in the bog as offerings.The remains of the boat were conserved, stabilized and put on display in the National Museum of Denmark since 1937. Because they were treated with alum at first and then later with PEG, the wood could no longer be radiocarbon dated, but a new excavation of the find site in 1987 found additional wood fragments that could be C-14 dated. The results date the boat to the 4th or 3rd century B.C.The recent study analyzed parts of the boat fragments of caulking and cordage that were collected in the original 1920s excavation, but had never been subjected to chemical preservation treatments. Modern technical analysis found the cordage is made from lime bast with long spin strands that would have kept the lashes pliable during construction of the boat and in later repairs.Taken together, the results of our analysis of the Hjortspring cordage illustrate the skill and sophistication of ancient Scandinavian boatbuilding techniques. It is clear that the cordage found in the boat was made by highly skilled craftspeople who were well versed in what must have been a long-standing boat building tradition. Due to the fact that the cordage fragments were untarred, it is possible they were kept on the boat for potential repairs. Such cordage could have been spliced into existing lines in the manner identified in our experimental trials. It is likely that both caulking material and cordage were kept on the ship in order to conduct repairs while at sea.The caulking materials contained the imprints of cordage, knots and plank seams as well as the partial fingerprint. They were subjected to gas chromatography mass spectrometry (GC-MS) which revealed the caulking was likely composed of a coniferous tar, probably pine, and far.The boat was waterproofed with pine pitch, which was surprising. This suggests the boat was built somewhere with abundant pine forests, says Mikael Fauvelle.Several scholars had previously suggested that the boat and its crew came from the region around modern-day Hamburg in Germany. Instead, the researchers now believe they came from the Baltic Sea region.If the boat came from the pine forest-rich coastal regions of the Baltic Sea, it means that the warriors who attacked the island of Als chose to launch a maritime raid over hundreds of kilometers of open sea, says Mikael Fauvelle.The print was likely left during repairs to the boat by a crew member. Researchers hope to extract ancient DNA from the caulking pitch to find out more about the seafarers who manned this vessel 2,300 years ago.