Scientists hope that the discovery will give them a better understanding of the way of life at the time.
Researchers from Kiel University, Germany, have discovered a wall in the Baltic Sea that is believed to be around 11,000 years old.
It dates back to the last Ice Age and is almost one kilometre long. At that time, the wall was probably located on a lake or bog, today it is 21 metres underwater.
According to geologists, the row of stones was used to hunt reindeer.
If the initial investigations are confirmed, the find would be the oldest human structure ever discovered in the Baltic Sea, which is surrounded by Denmark, Germany, Poland, Lithuania, Latvia, Estonia, Finland and Sweden.
Researchers hope the discovery will give them a better understanding of the way of life, organisation and hunting methods of humans at the time.