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 assumed 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 could possibly be the most important 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 digicam right down to the construction, which revealed a row of stones. “It was solely once we contacted the archaeologists that we understood it could possibly be one thing vital,” says Geersen.

There’s no cause or proof for a contemporary construction to have been constructed underwater at this web site, says group member Marcel Bradtmöller, an archaeologist on the College of Rostock, Germany. Nor can the group 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implies the wall was constructed when this space was dry land, which means it have to be between 8500 and 14,000 years outdated, says Bradtmöller. Earlier than that, the realm was lined by an ice sheet that may 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 comprises round 10 giant rocks as much as 3 metres throughout and weighing a number of tonnes, linked by greater than 1600 smaller stones largely beneath 100 kilograms in weight. The stones are positioned subsequent to at least one one other somewhat than on prime of one another, and the wall is lower than a metre excessive in most locations.

The large stones are all discovered the place the wall zigs or zags. So the group thinks the construction was constructed by linking giant stones that had been too heavy to maneuver with smaller stones that could possibly be shifted.

Bradtmöller believes it was most likely made by hunter-gatherers belonging to what’s often called the Kongemose tradition, named after a web site in Denmark the place artefacts corresponding to stone instruments have been discovered.

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

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

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

Though these partitions are sometimes low sufficient that animals corresponding to antelope might leap 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 comparable buildings. “In such circumstances, they have an inclination to run parallel to obstacles corresponding 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 risk with the newly found wall is that it was used to drive reindeer into the lake, the place they had been hunted from boats, says Bradtmöller.

It’s also attainable that there’s a second wall lined 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 this point, 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 could survive in a way 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 had been beforehand liveable.”

Fashionable actions corresponding to trawling, cable-laying and wind farm development 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 sort have been found in Europe, says Bradtmöller. He thinks it’s probably that many as soon as existed, however they had been destroyed by human actions.