Archaeologists in Denmark are recreating a puzzling Iron Age feature to understand better its purpose more than 2,500 years after it was built. Known as hulbælter in Iron Age, or “hole belts,” the structures consist of long rows of shallow pits that stretch across the landscape.
Dating to around 500–300 B.C., some extend for hundreds of meters, while others run for several kilometers. Researchers have identified nearly 50 examples across Denmark, particularly in central and western Jutland. Despite decades of study, archaeologists still do not know exactly why the pits were dug.
Hole belts remain one of Denmark’s oldest mysteries
The pits are not graves, ordinary postholes, or waste pits. Instead, they form organized belts three to six meters (9.8 to 19.6 feet) wide, with individual holes typically measuring only 30 to 40 centimeters (0.98 to 1.3 feet) deep.
Similar features have been reported in Sweden and the Netherlands, but they are far more common in Denmark. Their unusual layout suggests they were built for a specific purpose rather than as isolated features.
To investigate, researchers at the Saxo Institute at the University of Copenhagen have launched a large-scale experimental archaeology project.
Researchers rebuild an Iron Age landscape
Led by associate professor Henriette Lyngstrøm, the project brings together 30 archaeology students at Sagnlandet Lejre, an open-air research center and reconstructed Iron Age village.
The team is rebuilding a hole belt from scratch using reconstructed tools and ancient techniques. Researchers are measuring the time, effort, and coordination needed to create the features. The goal is to move beyond theory and test how the belts may have functioned in everyday life.
Digging reveals the scale of Iron Age labor
One part of the project focuses on reconstructed wooden spades based on Iron Age finds. Archaeologists once thought some of these tools may have been paddles. However, traces of soil, stones, and wear patterns suggest they were used for digging.
Archaeologists in Denmark are recreating mysterious 2,500-year-old Iron Age "hole belts" to uncover their purpose.
Were they defensive barriers, storage pits, boundary markers, or something else entirely?#Archaeology #IronAge #Denmark #AncientHistory pic.twitter.com/o3ZrDywejZ
— Tom Marvolo Riddle (@tom_riddle2025) June 8, 2026
Tests showed that wooden spades could create the pits, but the work was slow and physically demanding. The tools also required frequent sharpening.
The findings indicate that constructing long hole belts would have required planning, organization, and coordinated labor. Researchers say such projects likely involved leadership and cooperation within Iron Age communities.
Food storage theory gets a real-world test
Researchers also examined whether some pits could have been used for storage. Graduate student Angelyn Sørensen placed a chicken inside a ceramic jar buried in a reconstructed pit. On a day when air temperatures reached about 20 degrees Celsius, the meat warmed only slightly, rising from around 10 to 12 degrees.
The results suggest that covered pits could help moderate temperatures, although the experiment does not prove a storage function.
Experiments test the defensive barrier theory
The strongest results came from tests of the defensive theory. Earlier studies showed that sheep and cattle could cross similar pit zones without difficulty. However, when researchers staged mock combat exercises, the pits made movement more difficult for attackers.
Participants struggled to maintain balance, move quickly, and fight while crossing the uneven terrain.
Researchers stress that no single explanation has been confirmed. Still, the experiments show that the hole belts were carefully planned features that required labor, organization, and a clear purpose. Their exact role remains uncertain, but the project is bringing archaeologists closer to understanding one of Denmark’s most enduring Iron Age mysteries.
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