Ancient Warriors' Fingerprint Left Behind on Danish Island

About 2,400 years ago, before the emergence of the Roman empire, a small armada of boats approached the island of Als off the coast of southern Jutland in modern-day Denmark. The armada carried around 80 warriors armed with spears and shields. Some of them were officers, and these men carried iron swords. The seafarers had traveled across what is now the Baltic Sea in sleek plank boats some 20 meters long. The planks were sewn together as boats at this time did not use metal nails, and the seams were caulked (waterproofed) with tar. At some point along the voyage, they had stopped to repair their vessels. One of them left a partial fingerprint in the soft, newly applied caulking material between the plank seams. This sea-warrior—age and gender unknown—was inadvertently leaving a message for scientists (including me) who, more than two millennia later, would finally recognize thefingerprint's significanceusing cutting-edge technology. The small army was planning a quick marine assault on their enemies in Denmark—but their plans failed. Soon after they jumped on to the beach, these warriors were killed by the local defenders.