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Researchers believe the holes were used to store food and preserve it during the winter.
A team of archaeologists in Denmark is trying to unravel one of the country’s most persistent prehistoric enigmas: the function of so-called “hole belts“, long rows of shallow ditches that have cut across the Danish landscape for more than 2500 years.
Known in Danish as hollow beltsthese enigmatic landmarks date back to the early pre-Roman Iron Age, around 500-300 BC. Extending for hundreds of metres, the belts consist of rows of pits around 30 to 40 centimeters deep, forming corridors between three and six meters wide. They were almost 50 specimens identified throughout Denmark, mainly in Jutland, although similar structures have occasionally been found in Sweden and the Netherlands.
To discover its function, researchers from the University of Copenhagen’s Saxo Institute launched an experimental archeology project in the Iron Age village of Sagnlandet Lejre. Led by associate professor Henriette Lyngströmthe initiative involves archeology students in recreating a belt of holes using reconstructed Iron Age tools and techniques.
Rather than relying solely on excavation data, the project aims to understand how these structures were built and usedreproducing the physical conditions faced by Iron Age communities. Students shaped wooden tools, dug pits using reconstructed shovels, and measured the work needed to create the structures.
One experiment explored whether the pits could have been used to store food. Inspired by previous discoveries of pottery fragments in a belt of sinkholes in western Jutland, researchers placed a piece of chicken inside a ceramic container buried in a pit and monitored its temperature. Although the meat did not stay cold enough to meet modern food safety standards, testing suggested that covered pits could help moderate temperatures and potentially preserve food during colder seasons.
The findings could point to broader social implications. The construction of extensive ditch systems would have required leadership and collective effortsuggesting a level of hierarchy and organization within Iron Age communities.
The defensive function of pothole belts remains one of the leading theories. Although previous studies have found that the cattle could cross the ditches with easesimulated combat exercises conducted by Lejre’s team demonstrated that the uneven terrain posed challenges to the attackers while also favoring the defenders.
Although no definitive answer has emerged, experiments are narrowing the possibilities. The researchers conclude that the hole belts were carefully designed structures which served a deliberate purpose, reflecting the technical skills and social organization of Iron Age Denmark.
