Stone age wall found at bottom of Baltic Sea ‘may be Europe’s oldest megastructure’

The wall, which was built using smaller rocks to connect large boulders together, may have been used for hunting, researchers said. Photograph: Philipp Hoy

A stone age wall discovered beneath the waves off Germany’s Baltic coast may be the oldest known megastructure built by humans in Europe, researchers say.

The wall, which stretches for nearly a kilometre along the seafloor in the Bay of Mecklenburg, was spotted by accident when scientists operated a multibeam sonar system from a research vessel on a student trip about 10km (six miles) offshore.

Closer inspection of the structure, named the Blinkerwall, revealed about 1,400 smaller stones that appear to have been positioned to connect nearly 300 larger boulders, many of which were too heavy for groups of humans to have moved.

The submerged wall, described as a “thrilling discovery”, is covered by 21 metres of water, but researchers believe it was constructed by hunter-gatherers on land next to a lake or marsh more than 10,000 years ago.

While the purpose of the wall is hard to prove, scientists suspect it served as a driving lane for hunters in pursuit of herds of reindeer.

“When you chase the animals, they follow these structures, they don’t attempt to jump over them,” said Jacob Geersen at the Leibniz Institute for Baltic Sea Research in Warnemünde, a German port town on the Baltic coast.

“The idea would be to create an artificial bottleneck with a second wall or with the lake shore,” he added.

A second wall that ran alongside the Blinkerwall may be buried in the seafloor sediments, the researchers write in Proceedings of the National Academy of Sciences.

Alternatively, the wall may have forced the animals into the nearby lake, slowing them down and making them easy pickings for humans lying in wait in canoes armed with spears or bows and arrows.

Based on the size and shape of the 971 metre-long wall, Geersen and his colleagues consider it unlikely that it formed through natural processes, such as a huge tsunami moving the stones into place, or the stones being left behind by a moving glacier.

The angle of the wall, which is mostly less than 1 metre high, changes direction when it meets the larger boulders, suggesting the piles of smaller stones were positioned intentionally to link them up. In total, the wall’s stones are thought to weigh more than 142 tonnes.

If the wall was an ancient hunting lane, it was probably built more than 10,000 years ago and submerged with rising sea levels about 8,500 years ago.

“This puts the Blinkerwall into range of the oldest known examples of hunting architecture in the world and potentially makes it the oldest man-made megastructure in Europe,” the researchers said.

Geersen is now keen to revisit the site to reconstruct the ancient landscape and search for animal bones and human artefacts, such as projectiles used in hunting, which may be buried in sediments around the wall.