A low stone wall almost a kilometre lengthy has been discovered 21 metres under the floor of the Baltic Sea off the German coast. The wall is believed to have been constructed round 11,000 years in the past to channel reindeer into locations the place they may extra simply be killed, and may very well be the biggest Stone Age megastructure in Europe.

The invention was made by likelihood. In 2021, college students on a coaching train with geophysicist Jacob Geersen on the Leibniz Institute for Baltic Sea Analysis Warnemünde in Germany used a multibeam sonar to map the seafloor 10 kilometres offshore from the city of Rerik.

“Afterwards, within the lab, we realised that there was this construction that appears not pure,” says Geersen.

So in 2022, he and his colleagues lowered a digital camera all the way down to the construction, which revealed a row of stones. “It was solely once we contacted the archaeologists that we understood it may very well be one thing vital,” says Geersen.

There’s no motive or proof for a contemporary construction to have been constructed underwater at this web site, says staff member Marcel Bradtmöller, an archaeologist on the College of Rostock, Germany. Nor can the staff consider any pure course of that might create such a construction.

This implies the wall was constructed when this space was dry land, which means it have to be between 8500 and 14,000 years previous, says Bradtmöller. Earlier than that, the realm was coated by an ice sheet that will have destroyed any stone construction, whereas, later, rising sea ranges submerged the realm.

The wall runs alongside what was as soon as a lake. It incorporates round 10 massive rocks as much as 3 metres throughout and weighing a number of tonnes, linked by greater than 1600 smaller stones largely below 100 kilograms in weight. The stones are positioned subsequent to 1 one other fairly than on high of one another, and the wall is lower than a metre excessive in most locations.

The massive stones are all discovered the place the wall zigs or zags. So the staff thinks the construction was constructed by linking massive stones that have been too heavy to maneuver with smaller stones that may very well be shifted.

Bradtmöller believes it was in all probability made by hunter-gatherers belonging to what’s generally known as the Kongemose tradition, named after a web site in Denmark the place artefacts akin to stone instruments have been discovered.

The almost definitely rationalization is that the construction was used to channel reindeer, he says. “The speculation that, in the mean time, matches finest is a driving wall for looking.”

Whereas these hunter-gatherers are thought to have lived and travelled round in small teams, they may have assembled in bigger numbers on the lake when reindeer got here to the realm, says Bradtmöller.

Comparable low partitions, typically known as desert kites, have been discovered in lots of locations in Africa and the Center East, and likewise beneath the Great Lakes in North America. Some are as much as 5 kilometres lengthy, and it’s now broadly agreed they have been used for looking.

Though these partitions are usually low sufficient that animals akin to antelope may soar over them, they often keep away from them when operating in herds, says Marlize Lombard on the College of Johannesburg in South Africa, who has found related buildings. “In such circumstances, they have a tendency to run parallel to obstacles akin to low fences, as an alternative of traversing them,” she says.

Many desert kites include two partitions in a V-shape to funnel animals, however a single wall can nonetheless be an efficient driving line, says Lombard. One chance with the newly found wall is that it was used to drive reindeer into the lake, the place they have been hunted from boats, says Bradtmöller.

Additionally it is attainable that there’s a second wall coated by sediment close by, says Geersen. He plans additional investigations, together with diving, to attempt to discover direct proof of Stone Age individuals, however, to date, the researchers have been thwarted by unhealthy climate.

Different consultants additionally agree with their conclusions. “I believe the case is properly made for the wall as a synthetic construction constructed to channel actions of migratory reindeer,” says archaeologist Geoff Bailey on the College of York within the UK.

“Such a discover means that intensive prehistoric looking landscapes might survive in a fashion beforehand solely seen within the Nice Lakes,” says Vincent Gaffney on the College of Bradford within the UK. “This has very nice implications for areas of the coastal cabinets which have been beforehand liveable.”

Fashionable actions akin to trawling, cable-laying and wind farm building can destroy such websites, says Geersen, so extra exploration is required to seek out them earlier than they’re misplaced.

No different buildings of this type have been found in Europe, says Bradtmöller. He thinks it’s doubtless that many as soon as existed, however they have been destroyed by human actions.