A line of 1,673 stones running for 971 meters along the floor of the Baltic Sea was most likely built by Stone Age hunters to steer reindeer into an ambush. If that reading holds, it is one of the oldest known hunting structures on Earth and possibly the oldest human-made megastructure in Europe.
The wall sits 21 meters deep in the Bay of Mecklenburg, about 10 kilometers northwest of Rerik in Germany. A team led by marine geologist Jacob Geersen of the Leibniz Institute for Baltic Sea Research Warnemünde and Kiel University described it in a paper published in PNAS on February 12, 2024. The 16 authors include archaeologists from Rostock University and the Schleswig-Holstein State Museums.
Mapping the Blinkerwall stone by stone
The researchers first spotted the feature in September 2021 in high-resolution ship sonar data and named it the Blinkerwall. They then went back with an autonomous underwater vehicle carrying a multibeam echosounder, plus side-scan sonar, sediment cores and scientific divers.
Semi-automatic mapping counted 1,673 stones with a combined weight of about 142 tonnes. Most weigh well under 100 kilograms, but 288 are heavier. The largest, at roughly 11.4 tonnes, sits exactly where the wall changes direction, and the ten heaviest stones all sit at such bends.
The wall is usually under 1 meter high and under 2 meters wide. Just north of it is a 10-meter strip with noticeably fewer loose stones, which the authors read as the spot where builders gathered their material and moved it a short way downhill.
Why nature probably did not build it
The team worked through the natural explanations one by one. Tsunamis can move large boulders but are not known to lay them in a neat kilometer-long line. Moraines and eskers do not fit the wall’s position, orientation, small size or lack of gravel. Ice pushing stones onto a shoreline would have required stones exposed in the basin to the south, which had already been buried under lake sediments by the relevant time.
Modern causes also looked unlikely. The nearest undersea power cable lies more than 3 kilometers north, in soft sediment, and cannot explain the wall’s bends.
Sediment cores helped with the timing. The wall runs along the shore of a former lake or bog, whose youngest phase dates to about 9,100 years ago. Sea-level reconstructions show the area drowned during the Littorina transgression, about 8,500 years ago. That rules out farmers and points to hunter-gatherers who roamed the region after the ice sheet retreated.
A drive lane for reindeer herds
The authors argue the most plausible use was as a drive lane. Reindeer are attracted to linear features and tend to follow them, and studies suggest east-west migration routes in the region, matching the wall’s direction. Hunters could have pushed animals along the wall into the lake or a dead end, perhaps using the big boulders as hunting blinds.
The closest comparison is “Drop 45,” a submerged drive lane in Lake Huron, though that structure is only about 30 meters long. Reindeer were regularly present in the area only until about 9,800 years ago, so if the wall was built for them, it dates to the end of the last ice age or the very start of the Holocene.
The authors are clear that dating such structures is hard because artifacts and carcasses are usually missing, and the hunting-blind idea still needs testing by divers. Their next targets are other till ridges in the bay at around 20 meters depth, where similar walls may still lie uncovered.
Study Details:
- Title: A submerged Stone Age hunting architecture from the Western Baltic Sea
- Authors: Jacob Geersen, Marcel Bradtmöller, Jens Schneider von Deimling, Peter Feldens, Jens Auer, Philipp Held, Arne Lohrberg, Ruth Supka, Jasper Justus Lutz Hoffmann, Berit Valentin Eriksen, Wolfgang Rabbel, Hans-Jörg Karlsen, Sebastian Krastel, David Brandt, David Heuskin, Harald Lübke
- Journal: Proceedings of the National Academy of Sciences (PNAS)
- Publication Date: February 12, 2024
- DOI: 10.1073/pnas.2312008121