Though the mysterious standing stones in Wiltshire, England look intact from the outside, three fragments of Stonehenge have been missing since 1958. Now, more than 60 years after it was taken, BBC reports that one of the pieces has been returned to the site.

The history of Stonehenge stretches back to 3000 BCE, and archaeologists have studied the site since the 17th century. In 1958, a team of archaeologists raised a collapsed trilithon—three stones that had been arranged into an upright shape—and contracted a diamond-cutting company to restore it. Cores were drilled through a cracked stone and metal rods were inserted to stabilize the structure.

Robert Phillips was one of the employees tasked with drilling into the stone 60 years ago. Workers extracted three, 3-foot-long stone cores from the pillar, and when the job was done, Phillips decided to take one of the pieces home with him. He's kept it all this time, even holding onto when he moved from England to Florida, and the day before his 90th birthday last year, he made the choice to return it to its home.

Though the core is just a fragment of the multi-ton stone circle, it could hold important clues regarding the site's origins. Unlike the rocks' weathered exteriors, the stone core is reportedly pristine, and it can be subject to analysis that would be hard to perform on the intact stones. Archaeologists hope the tests will shed further light on where the ancient rocks originated.

The rediscovered artifact may clarify some Stonehenge mysteries, but the question of where the other two stone cores ended up remains unanswered.

[h/t BBC]