Every year, roughly one million tourists flock to Stonehenge, the iconic prehistoric monument in southwest England, to experience the eerie aura of this 5,000-year-old ritual site. Yet despite its immense popularity, Stonehenge still has a few mysteries up its sleeve: scientists have discovered huge underground shafts that may form the most massive prehistoric structure known in Britain.
A team of archaeologists found “new evidence for hitherto unknown features or monumental structures” about two miles northeast of Stonehenge, according to a study published on Sunday in the journal Internet Archaeology.
Thousands of years ago, people at this site dug out these large pits, which are about five metres deep (roughly three times the height of the average modern person) and 10 metres wide. They are arranged in a partial concentric ring with a diameter that stretches across more than a mile and encircles Durrington Walls, a settlement that dates back at least 4,000 years and which may have been the place where Stonehenge’s builders resided.
The discovery “represents an elaboration of the monument complex at a massive, and unexpected, scale,” according to the study, which was led by University of Bradford archaeologist Vincent Gaffney.
Gaffney and his colleagues were able to detect the remains of about 20 of these pits thanks to remote-sensing technologies like ground-penetrating radar and LiDAR that can non-invasively probe underground structures. These techniques revealed the shafts, each of which looks like “a disc of enhanced magnetic readings”, according to the study.
“The discovery of the Durrington pit circuit is surprising and confirms the capacity of remote sensing projects to contribute to our understanding of large-scale landscape structuration during the Neolithic and Bronze Ages,” the team said in the research.
“The data also hint at evidence for the maintenance of this monumental structure into the Middle Bronze Age which, if correct, would have significant implications for our understanding of the history and development of monumental structures across the Stonehenge landscape,” the researchers added.
The immensity of the pit structure, combined with the tantalizing hints that it may have been carefully maintained, raises the obvious question of its significance and function for its creators and tenders. While similar rounded structures are found in other ancient earthworks, the scale of the Durrington pit circuit is unparalleled by anything else in Britain.
Gaffney and his colleagues speculate that the pits may have been inspired by the same celestial mythologies and astronomical alignments that were clearly expressed in the rock placements at Stonehenge. For instance, the pits may have been laid out as tallies, or measurement points, with a ritual function for people walking between them.
“Archaeologically, some early tallies do appear to have linkages with astronomic, and, presumably, cosmological cycles,” the team said in the paper. “Without recourse to the extremes of numerology, it is conceivable that the act of pacing out a notional pattern on the ground might well have reinforced perceived cosmological linkages and these, in turn, may have been inscribed into the landscape through the massive pits found at Durrington.”
It will take a lot more research to understand why, how, when, and for whom this pit circuit was constructed. However, the spectacular find has made one thing clear: Stonehenge still has many secrets left to spill.
This article originally appeared on VICE US.