Stonehenge, one of Britain's most enigmatic prehistoric monuments, has a secret "sister" that is even older, scientists have revealed.
Archaeologists have re-dated the Flagstones monument in Dorset to 3200 BC, making it several centuries older than previously thought.
The circular enclosure could have been a "prototype" for Stonehenge, which was built around 2900 BC.
New research from the University of Exeter and Historic England has uncovered this remarkable connection between the two ancient sites.
Archaeologists have re-dated the Flagstones monument in Dorset to 3200 BC, making it several centuries older than previously thought
PA
Lead author of the study Dr Susan Greaney said: "The 'sister' monument to Flagstones is Stonehenge, whose first phase is almost identical, but it dates to around 2900 BC."
"Could Stonehenge have been a copy of Flagstones? Or do these findings suggest our current dating of Stonehenge might need revision?" she added.
The similarity between the two sites had previously led researchers to believe they were built around the same time.
However, radiocarbon dating has revealed Flagstones' true age.
The Flagstones monument was discovered in the 1980s during construction of the Dorchester bypass.
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It consists of a 100-metre-diameter circular ditch made of intersecting pits and likely an earthwork bank.
Today, half the site lies beneath the bypass, with the remainder under Max Gate, Thomas Hardy's former home.
At least seven individuals were buried at the site, including a cremated adult and three children who had not been cremated.
The site is now a scheduled monument with finds preserved at the Dorset Museum.
Dr Greaney explained: "Flagstones is an unusual monument, a perfectly circular ditched enclosure, with burials and cremations associated with it."
Handout artist impression issued by University of Exeter of an aerial view of the original excavation of the Flagstones monument
PA
"In some respects it looks like monuments that come earlier, which we call causewayed enclosures, and in others it looks a bit like things that come later that we call henges."
"But we didn't know where it sat between these types of monuments and the revised chronology places it in an earlier period than we expected."
By measuring radioactive carbon-14 in biological materials from the site, researchers established a new timeline for Flagstones.
The earliest activity, including digging of pits, took place around 3650 BC.
After several centuries, the circular ditched enclosure was created around 3200 BC, with burials placed within it immediately afterwards.
In contrast, construction at Stonehenge began around 3000 BC with a circular ditch.
The famous sarsen stones were only erected around 2500 BC to form the monument recognisable today.
Researchers believe Stonehenge might have "directly replicated" the form of the earlier Flagstones monument.
Both sites served as burial grounds, with Stonehenge containing 64 cremations and an estimated 150 individuals in total.
