Two millennia or so ago, sailing ships, grazing animals, and people—hunting, gathering, dancing—were carved into cave walls, then obscured, slowly, by layers of moss. Ultimately, they were lost to time.
Or lost until last month, when a team of researchers surveying the western Swedish province of Bohuslän uncovered the ancient artwork. The carvings, or petroglyphs, were made around 2,700 years ago, according to the Foundation for Documentation of Bohuslän’s Rock Carvings. They measure around three-meters high and decorate a steep rock face that once formed the edge of an island before sea levels dropped around 40 feet over several centuries.
The team has since speculated that the artists reached the rock by boat, or constructed a sort of scaffolding over ice. (The researchers used scaffolding themselves to inspect the artworks.) The deep carvings were made by striking stones against the granite rock to reveal a brilliant white underlayer that would have been visible for several miles.
“What makes the petroglyphs completely unique is that they are located three meters above today’s ground surface,” the foundation wrote in a statement. “The motifs lie on an even line that follows the height of the sea surface from approximately 700 to 800 BCE. The motifs are also stylistically consistent with this time period.”