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More than 2,000 years ago, a mysterious band of attackers descended on an island called Als off Denmark’s coast. Locals seem to have successfully fought back against the marauders and dumped one of their boats—chock-full of weapons—into a bog to celebrate their defeat of the invaders.
Remnants of this ancient battle were unearthed in the 1880s by people digging for peat in the Hjortspring bog on Als. Researchers excavated the invaders’ boat in the 1920s and recovered nearly half of it, which provided enough material for a full reconstruction. This ancient wooden plank boat is the only intact vessel of its kind ever discovered in Scandinavia, and it resembles boats depicted around a millennium earlier in Bronze Age rock art.
The bog boat still begs a major question: Where did the invaders actually invade from, and when? Researchers have offered a few guesses to solve this maritime mystery, suggesting the invading party came from the nearby island of Funen, or even the northern coast of Europe. The weapons found within the boat look like those used throughout northern Europe during the period, though wooden containers on board resemble ancient ones previously found in countries including modern-day Denmark, Germany, and Sweden. As for attaching a date to the artifacts, the chemicals previously applied to the boat make it unfeasible to perform radiocarbon dating on the wood, though some wooden fragments have been found nearby in the bog that were dated back to the fourth or third centuries B.C.
Now, a team from Sweden and Denmark have drawn compelling hints from bits of the boat that haven’t yet been studied by scientists—caulking and cord materials. They found that the caulk was composed of animal fat and pine pitch, according to a paper recently published in PLOS One. Yet Denmark didn’t have many pine forests at the time, a key detail that might illuminate the identities of these vanquished warriors.
The pine pitch could’ve arrived to areas near Als through trade, but this finding could also mean that the boat was constructed east of Denmark somewhere along the shores of the Baltic Sea, where there were more pine forests at the time. That means the invaders may have traveled hundreds of miles, possibly from parts of Poland or Sweden, for example, the authors suggested. Carbon dating of the cords and caulk also pointed to origins in the fourth or third centuries B.C., confirming earlier estimates.
Read more: “We Need to Talk About Peat”
That wasn’t all the researchers found—they also encountered a partial human fingerprint in the caulking material. “This remarkable fingerprint provides a direct link to the ancient seafarers who used this boat,” the authors wrote. It’s tricky to discern who left this impression because “these ridge sizes fall within average distributions for both adult male and females as well as for juvenile adults, making it difficult to say much about the individual who produced the print.”
If the attackers indeed came from a far-off land, they noted, this means that the Als invasion was planned in advance and highly organized. This suggests that political battles raged throughout Scandinavia long before the Viking period that was characterized by raucous raids.
Now, the authors want to sample potential traces of DNA from the caulking to learn more about the seafarers, and they hope the new findings can “open the door to finally solving the mystery of the boat’s provenance.” 
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Lead image: Boel Bengtsson
