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It is a mystery that has baffled geologists and historians for centuries... how were the Stonehenge rocks transported from Wales' Preseli mountains to their resting place 120 miles away.

Scientists are today one step closer to solving the 4,000-year- old mystery after making their most significant discovery in 15 years.

Of the six to eight different bluestone types found in the inner circle of rocks on Salisbury Plain, only one, the so- called "spotted dolerite", was convincingly traced to the Mynydd Preseli area in north Pembrokeshire in the early 1920s.

But modern technology has now assisted geologists at Amgueddfa Cymru - National Museum Wales - in creating a "fingerprint" for one of the other rock types found in Wiltshire.

And that "fingerprint" has been identically matched to stones found in an area north of the Mynydd Preseli range, in the vicinity of Pont Saeson.

The discovery means archaeologists are now a step closer to retracing the footsteps of Neolithic engineers who moved the stones in the first place.

Dr Richard Bevins, Keeper of Geology at Amgueddfa Cymru, said: "The outer circle of Stonehenge is made up from stones sourced locally in Salisbury Plain but it is the mismatch of rocks found in the inner circle that have caused so much mystery.

"We have known for some time that spotted dolerite came from Preseli but of those remaining stones we think that six to eight more may have come from Pembrokeshire, until now though we haven't been able to be sure because the stones are very fragile and we didn't previously have the technology to extract their DNA."

Dr Bevins added: "Theoretically if we could trace the source of the other rhyolites (rock types) we could create a map with six or more locations pinpointing where each stone was sourced.

"Archeologists could then essentially see the route that was taken by these people, they could re-trace those steps, set up archaeological digs and make who knows how many new discoveries.

"In terms of looking at where the stones came from this is the most important discovery we've made regarding Stonehenge in 10 or 15 years."

Dr Bevins, in partnership with Dr Rob Ixer at the University of Leicester and Dr Nick Pearce of Aberystwyth University, made the discovery by analysing microscopic crystals found in the rock, vaporising them and analysing the gases found as a result.

The composite of gases makes up the rock's DNA which can then be matched to other rock forms.

Sourcing the rhyolites also provides the opportunity for new thoughts on how the stones might have been transported to the Stonehenge area.

Much of the archaeology in recent years has been based on the assumption that Neolithic Age man had a reason to transport bluestones all the way from West Wales to Stonehenge and the technical capacity to do it.

Dr Bevins said: "It has been argued that humans transported the spotted dolerites from the high ground of Mynydd Preseli down to the coast at Milford Haven and then rafted them up the Bristol Channel and River Avon to the Stonehenge area.

"However, the outcome of our research questions that route, as it is unlikely that they would have transported the Pont Saeson stones up slopes and over Mynydd Preseli to Milford Haven, we would assume that they would not carry the rocks up and over a steep mountain range.

"If humans were responsible then an alternative route might need to be considered."

Some believe that the stones were transported by the actions of glacier sheets during the last glaciation and so the Pont Season discovery will need appraising in the context of this hypothesis.

Mike Parker Pearson, Professor of Archaeology at Sheffield University, added: "This is a hugely significant discovery which will fascinate everyone interested in Stonehenge.

"It forces us to re-think the route taken by the bluestones to Stonehenge and opens up the possibility of finding many of the quarries from which they came.

"It's a further step towards revealing why these mysterious stones were so special to the people of the Neolithic."