Timewatch animation revealing the history of Stonehenge
The first excavation inside the ring at Stonehenge in more than four decades gets under way on Monday.
The two-week dig will try to establish, once and for all, some precise dating for the creation of the monument.
It is also targeting the significance of the smaller bluestones that stand inside the giant sarsen pillars.
Researchers believe these rocks, brought all the way from Wales, hold the secret to the real purpose of Stonehenge as a place of healing.
The excavation at the 4,500-year-old UK landmark is being funded by the BBC. The work will be filmed for a special Timewatch programme to be broadcast in the autumn.
The researchers leading the project are two of the UK's leading Stonehenge experts - Professor Tim Darvill, of the University of Bournemouth, and Professor Geoff Wainwright, of the Society of Antiquaries.
We believe that this dig has a chance of genuinely unlocking part of the mystery of Stonehenge
They are convinced that the dominating feature on Salisbury Plain in Wiltshire was akin to a "Neolithic Lourdes" - a place where people went on a pilgrimage to get cured.
Some of the evidence supporting this theory comes from the dead, they say.
A significant proportion of the newly discovered Neolithic remains show clear signs of skeletal trauma. Some had undergone operations to the skull, or had walked with a limp, or had broken bones.
Modern techniques have established that many of these people had clearly travelled huge distances to get to south-west England, suggesting they were seeking supernatural help for their ills.
But Darvill and Wainwright have also traced the bluestones - the stones in the centre of Stonehenge - to the exact spot they came from in the Preseli hills, 250km away in the far west of Wales.
Neolithic inscriptions found at this location indicate the ancient people there believed the stones to be magical and for the local waters to have healing properties.
Darvill and Wainwright hope the dig will demonstrate such beliefs also lay behind the creation of Stonehenge, by showing that the make-up of the original floor of the sacred circle at the monument is dominated by bluestone chippings that were purposely placed there.
The last dig inside the Unesco World Heritage monument was in 1964
The dig will also provide a more precise dating of the Double Bluestone Circle, the first stone circle that was erected at Stonehenge.
The original setting for this circle is no longer visible. The bluestones seen by visitors today are later re-erections.
Archaeologists tried to date the first circle in the 1990s and estimated that it was put up at around 2,550BC; but a more precise dating has not been possible.
Principally, this is because materials removed in earlier excavations were poorly recorded and cannot be attributed with any certainty to specific features and deposits.
The 3.5m by 2.5m trench that will be excavated in the new effort will aim to retrieve fragments of the original bluestone pillars that can be properly dated.
The BBC's Jon Kay talks to Geoff Wainwright about the dig
The BBC-funded excavation goes ahead with the full support of English Heritage, which manages the site for the nation.
"Theories about Stonehenge are cheap; proof is precious," commented BBC Timewatch editor, John Farren.
"I'm delighted that Timewatch, the BBC's flagship history programme, is able to offer the possibility for some hard scientific proof to further our knowledge of the dating of Stonehenge and to bolster this remarkable new theory.
"It's taken us 18 months' hard work to get all the elements for the dig in place."
Professor Wainwright added: "This small excavation of a bluestone is the culmination of six years of research which Tim and I have conducted in the Preseli Hills of North Pembrokeshire and which has shed new light on the eternal question as to why Stonehenge was built.
"The excavation will date the arrival of the bluestones following their 250km journey from Preseli to Salisbury Plain and contribute to our definition of the society which undertook such an ambitious project. We will be able to say not only why but when the first stone monument was built."
Dr Simon Thurley, chief executive of English Heritage, commented: "Very occasionally, we have the opportunity to find out something new archeologically - we are at that moment now.
"We believe that this dig has a chance of genuinely unlocking part of the mystery of Stonehenge."
BBC Timewatch will follow the progress of the Stonehenge dig over the course of the next two weeks. Catch daily text and video reports on the programme's website. A BBC Two documentary will be broadcast in the autumn and will detail the findings of the investigation
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