Archaeologists say they have found scientific proof that humans created a ring of deep pits near Stonehenge more than 4,000 years ago. The pits at Durrington Walls in Wiltshire could reportedly be “one of the largest prehistoric structures in Britain, if not the largest prehistoric structure.”

The series of massive pits were first discovered in 2020. Several are about 30 feet wide and reach 15 to 20″ feet into the ground. The circle of pits, which the builders set at regular intervals and date to the Late Neolithic period, covers an area around 1.24 miles wide.

“They can’t be occurring naturally,” study lead author Vincent Gaffney, an archaeologist at the University of Bradford, told the Guardian. “It just can’t happen. We think we’ve nailed it.”

The archaeologists used several scientific techniques, including electrical resistance tomography, radar, magnetometry and sedDNA, to analyze the pits. Their findings convinced them that humans constructed them.

“The circle is pretty accurate. It suggests that people were pacing the distances out to make sure that the pits were aligned at the same distance all the way around, as the distance from the henge to the earlier enclosure,” Gaffney told the BBC.

Researchers have theories about the purpose of the pits, but no proof yet

The archaeologists couldn’t determine the exact purpose of the pits near Stonehenge. They searched for looked for traces of seeds and water or anything else that might indicate the pits’ purpose and found nothing. Researchers have also discovered similar networks of large pits in other locations across Britain. Their purpose is also a bit of a mystery.

One theory is that the pits at Durrington Walls were some sort of border. Perhaps the builders of the pits were “inscribing something about their cosmology, their belief systems, into the earth itself in a very dramatic way.” Gaffney added that they may have been attempting to connect to the underworld.

“These features were not simply dug and abandoned – they were part of a structured, monumental landscape that speaks to the complexity and sophistication of Neolithic society,” Gaffney said in a press release discussing the study.