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A megastructure found in the Baltic Sea may represent one of the oldest known hunting structures used in the Stone Age – and could change what is known about how hunter-gatherers lived around 11,000 years ago.
Researchers and students from Kiel University in Germany first encountered a surprising row of boulders located about 69 feet (21 meters) underwater during a marine geophysical survey on the seafloor of Mecklenburg Bay, about 6 miles (9, 7 kilometers) off the coast of Rerich, Germany.
The discovery, made in the fall of 2021 aboard the research vessel RV Alkor, revealed a wall made of 1,670 stones that stretches for more than half a mile (1 kilometer). The stones that connected several large stones were almost perfectly aligned, making it seem unlikely that nature formed the structure.
After the researchers notified the State Office for Culture and Monument Preservation of Mecklenburg-Vorpommern about their find, an investigation began to determine what the structure might be and how it ended up at the bottom of the Baltic Sea. Diving teams and an autonomous underwater vehicle were used to explore the site.
The team found that the wall was probably built by Stone Age reindeer hunting communities more than 10,000 years ago.
A study describing the structure was published Monday in the journal Proceedings of the National Academy of Sciences.
“Our studies show that the natural origin of the underwater rock wall, as well as construction in modern times, for example in connection with the laying of underwater cables or collecting stones, is not very likely. The methodical arrangement of the many small stones that connect the large, stationary stones speaks against this,” said lead study author Dr. Jacob Giersen, a senior scientist at the Leibniz Institute for Baltic Sea Research in Germany, in a statement.
The wall was probably built more than 10,000 years ago along the shore of a lake or marsh, according to the study. The rocks were abundant in the area at the time, left by glaciers that moved across the landscape.
But studying and dating submerged structures is incredibly difficult, so the research team had to analyze how the region developed to determine the approximate age of the wall. They collected sediment samples, created a 3D model of the wall and virtually reconstructed the landscape where it was originally built.
Sea levels rose significantly after the end of the last ice age about 8,500 years ago, which would have flooded the wall and large parts of the landscape, according to the study’s authors.
But things were different nearly 11,000 years ago.
“At that time, the entire population of northern Europe was probably less than 5,000 people. One of their main food sources was reindeer herds that migrated seasonally across the sparsely vegetated postglacial landscape,” study co-author Dr. Marcel Bradtmöller, assistant professor of prehistory and early history at the University of Rostock in Germany, said in a statement. “The wall was probably used to guide reindeer into a narrow area between the adjacent lake shore and the wall, or even into the lake, where Stone Age hunters could more easily kill them with their weapons.”
P. Hoy, University of Rostock, model created using Agisoft Metashape by J. Auer, LAKD MV
The researchers practically reconstructed how the wall probably appeared during the Stone Age.
Hunter-gatherers used spears, bows and arrows to catch their prey, Bradtmoeller said.
A secondary structure may have been used to create the barrier, but the research team has yet to find any evidence of that, Geersen said. However, it is likely that hunters directed the deer to the lake because the animals are slow swimmers, he said.
And the hunter-gatherer community seemed to realize that the deer would follow the path created by the wall, the researchers said.
“It appears that animals are attracted to such linear structures and that they prefer to follow the structure rather than try to cross it, even if it is only 0.5 meters (1.6 feet) high,” Geersen said.
The discovery changes the way researchers think about highly mobile groups like hunter-gatherers, Bradtmoeller said. Building a massive permanent structure like the wall suggests these regional groups may have been more location-focused and territorial than previously thought, he said.
The discovery marks the first Stone Age hunting structure in the Baltic Sea region. But other comparable prehistoric hunting structures have been found elsewhere in the world, including the United States and Greenland, as well as Saudi Arabia and Jordan, where researchers have found traps known as “desert kites.”
Stone walls and hunting blinds built to hunt caribou were previously found at the bottom of Lake Huron in Michigan and found at a depth of 98 feet (30 meters). The construction and location of the Lake Huron wall, which includes a lake shore on one side, is most similar to the Baltic Sea wall, the study authors said.
In the meantime, scientists are continuing their investigation in the Baltic Sea using sonars and probes, as well as planning future dives to search for archaeological finds. Only by combining the expertise of those in fields such as marine geology, geophysics and archeology are such discoveries possible, Giersen said.
Understanding the location of lost structures and artifacts on the seafloor is key as demand for offshore areas increases due to tourism and fishing and the construction of pipelines and wind farms, he said. And other undiscovered treasures on the bottom of the Baltic Sea could potentially shed more light on ancient hunter-gatherer communities.
“We have evidence of the existence of comparable stone walls elsewhere in (Mecklenburg Bay). They will also be systematically investigated,” study co-author Dr. Jens Schneider von Deimling, a researcher in the Marine Geophysics and Hydroacoustics group at Kiel University, said in a statement.