A mysterious set of standing stones in southwest England, lost since the 1990s, will remain missing a little longer. But thanks to the search for them, archaeologists have new data about the ancient landscape on which the stones were built, which may shed light on the culture that left them behind.

Sometime between 4,500 and 3,000 years ago, people living in southwest England near present-day Devon carefully arranged 18 small pieces of sandstone—each about a foot high and nine inches wide—in two parallel rows. The rows were 113 feet long, with six feet of space between the stones. Their ancient builders settled each stone into a carefully dug pit, and the stones stood for thousands of years on Isley Marsh, a low-lying stretch of land near the sea. But now no one has seen the stones in over 20 years.

The disappearing stones

A power station was built near the stones in the 20th century. Its construction had changed the flow of water and sediment through the Taw Estuary and Isley Marsh, but its operations helped keep the Taw Estuary’s channel relatively clear of silt. When the power station shut down in the 1980s, the silt began flowing into the marsh with each incoming tide, slowly burying the ancient standing stones.