To the untrained eye, the modest gray boulder in a Dorset, England, field would be easy to miss.

Jim Rylatt and Anne Teather nearly didn’t spot it. The two directors of Past Participate CIC, a local history and archaeology nonprofit, were exploring the Valley of Stones national nature reserve when they stumbled upon it.

“It’s a relatively unprepossessing boulder on one side,” Rylatt tells the Guardian’s Steven Morris. But then he noticed the smooth, shiny section on the other side. This stone, he realized, was no ordinary boulder.

It was actually a polissoir, a French word meaning “polisher.” Polissoirs were used by Neolithic groups as tools to sharpen axes—and although the tools have been commonly found across France, this is only the second undisturbed polissoir found in its original position in all of England.

The polissoir is more than 5,000 years old, placing it squarely in the Neolithic period in Britain, which spanned from around 4300 to 2000 B.C.E. At the time, stone axes were critical tools for early farming groups.

“These stones rarely survive, but would have been extremely important to Neolithic people, as without axes they could not have cleared woodland and farming would have been impossible,” says Rylatt in a statement.

Evidence shows that ax heads sometimes traveled far from the places they were quarried, but researchers are not entirely sure about the details: Did trade systems exist? Did the axes’ owners carry them on long journeys?

Regardless, this polissoir was found near the site of a former routeway, meaning it likely didn’t belong to a stationary group.

“This was not necessarily a place of settlement but a place people came to and moved through,” Teather tells the Guardian.

Neolithic ax heads were commonly made of materials like flint, volcanic tuff and granite. Although no ax heads have been found in the immediate vicinity, Historic England is launching a more extensive archaeological survey as a result of the find.

“This is a hugely exciting and rare discovery in this little understood historic landscape, which is giving us an opportunity to explore the use of the stone, and the communities who were using it,” says Sasha Chapman, inspector of ancient monuments at Historic England, in a statement.

Rylatt is excited about his discovery—and the insights the unassuming polissoir will provide into the area’s history.

“I didn’t realize how rare they actually were!” Rylatt tells Jamie Guerra of Greatest Hits Radio Dorset. “The last one was found in 1963, so you’re looking at 2086 before the next one is likely to come around.”