Archaeologists trying to uncover the mystery of Stonehenge have been digging around the wrong hill for almost a century.
Teams of archaeologists have spent the past 90 years scouring the Preseli Hills in Pembrokeshire to find the source of the prehistoric monument's iconic 'blue stones'.
Scientists believed the 11 stones used to construct the ancient site came from a hill called Carn Menyn, but geologists have since discovered they actually came from another hill - just over a mile away - called Carn Goedog.
A paper published by academic H.H Thomas in 1923 was the first to suggest the stones came from Pembrokeshire.
The region of the Preseli Hills in the Pembrokeshire Coast National Park is renowned for blue stones that resemble those used to build Stonehenge.
Thomas claimed the particular dolerites that make up the ancient site came from a hill called Carn Menyn, and archaeologists have been digging on this location for the past 90 years in search of human activity.
However, researchers from the National Museum of Wales, University College London and Aberyswyth University recently wanted to pinpoint the exact location.
They X-rayed the 11 bluestones in Amesbury and discovered they more equally matched stones found on a hill called Carn Goedog - just a mile away from Carn Menyn.
They can then start trying to discover if prehistoric man cut the 11 stone monoliths from the hill and transported them to the prehistoric site, or if they were carried there by glaciers during the last Ice Age.
Dr Richard Bevins from the National Museum of Wales is a leading authority on volcanic rocks and has been studying the Preseli Hills since he was a PhD student in the late 1970s.
Working with Dr Rob Ixer of University College London and Professor Nick Pearce of Aberystwyth University, Dr Bevins used a paper published by academic H.H Thomas in 1923 as their starting point.
Thomas's paper was the first to put forward the theory that the blue stones of Stonehenge came from Pembrokeshire.
In particular, it said they came from a Preseli Hill called Carn Menyn and ever since then archaeologists have assumed that to be the case.
But Dr Bevins said: 'When Thomas was doing his research, it wasn't possible for him to be as precise as we can now.
'By X-raying dolerites from Stonehenge and comparing them with dolerites from Carn Goedog, we know with some degree of certainty that is where the blue stones originated.
'This is an incredibly exciting project and we got confirmation last week that our findings have been verified,' continued Dr Bevins. 'Getting such positive feedback was a great relief.
Stonehenge was built and altered over a period of about 1,000 years, starting around 2,600 BC.
There are two types of stones at Stonehenge - the larger sarsens and the smaller outer rings of blue stones.
The bluestones come from the Preseli Hills of Pembrokeshire but how the stones were transported over 160 miles to Stonehenge remains a mystery.
Dr Bevins said there were competing theories but now archaeologists could finally solve the mystery now they've uncovered the stones' precise source.
He said: 'Some have suggested they were transported by humans south to Milford Haven, put on boats and taken by sea to a point from which they were carried to Salisbury Plain.
'Others have suggested they may have been transported naturally by rock movements during the last Ice Age. It's not for me to say which of the theories is correct.
'If humans were involved in taking the stones, there should be some evidence of human activity at the site. But if they were transported during the last Ice Age, physical evidence should be present.
Dr Bevins and the team of geologists will have their peer-reviewed paper published by the Journal of Archaological Science next year.