Clues to history hidden in stones

New research throws open the origins of Stonehenge. Were its stones transported by man or glacier?
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Imagine a civilisation without metal, plastic or even concrete. It sounds impossible, but for most of human history, the hi-tech material for building, tools or machinery was stone. Now a team at the Open University is using new techniques to decipher the clues to our past, hidden in old stones, including controversial Stonehenge.

Dr Olwen Williams-Thorpe and senior research fellow Dr Phil Potts, of the OU's Earth Sciences department, work with statistician Professor Chris Jones to trace the quarry sources of stone artefacts. These range from prehistoric axes to Roman columns, and their specially adapted equipment allows them to examine the objects without causing them damage. Seeing how far the artefacts have moved from their source reveals patterns of communication and trade from past millennia. Dr Williams-Thorpe explains: "Trade in artefacts is one of the very few ways we can reconstruct the contact between different human communities for the prehistoric period. Even for the Roman Period, the written records are very incomplete, so it is enormously useful. We have looked at artefacts from the upper Palaeolithic (Old Stone Age) through to the medieval period."

One of the few archaeological scientists in the country, Dr Williams-Thorpe was the among the first to graduate from Britain's first Archaeological Science Masters course in 1975, and subsequently obtained an Archaeological Science DSc from the OU.

She and the team use technology developed for geologists prospecting for minerals, including gamma ray spectrometry, a portable X-ray machine and a device which measures magnetism in the rock. "Geologists are usually looking at a large rockface whereas we are looking at small objects. We have done a huge amount of development work to make these techniques applicable to artefacts," she says.

Testing provides a chemical or geophysical "fingerprint" of the artefact, from which it is possible to work out not merely what type of stone it was made from but, in many cases, the specific outcrop from which it was quarried. As well as scientific analysis, the process involves detective work, matching the "fingerprint" to known prehistoric sources of stone.

Her investigations have covered areas as diverse as trade in axes during the Stone Age, and the source of Roman columns in Windsor Great Park. They reveal that globalisation is nothing new – items were traded across many hundreds of miles even as far back as the Stone Age, she says. "Shipwrecks are particularly fascinating. We looked at a Greek ship which was wrecked off Majorca with a cargo of millstones; by studying where the millstones came from we could trace the route the ship took."

The team's latest project takes them into an area which is highly controversial – the construction of Stonehenge. Using a £21,000 grant from the Leverhulme Trust, they are analysing a group of Stone Age axes believed to be made out of the same bluestone used to build the stone circle which is the oldest part of Stonehenge.

Bluestone, more scientifically known as spotted dolerite, is found only in Preseli in Wales. Arguments have raged for years between those who believe the stones were brought to Stonehenge by Stone Age people using rafts and ropes, and others who say they were transported naturally by prehistoric glaciers.

But why should our ancestors have gone through the effort of hauling heavy stones all the way from Wales to Salisbury Plain? Dr Williams-Thorpe explains: "There were other suitable stones between Wales and Salisbury Plain that could have been brought, but the idea is that this stone was – "magic" may be too strong a word – but it had some special significance." The idea that our neolithic and Bronze Age ancestors favoured the same stone when making their axes has been used to add support to the "magical bluestone" theory. But the team's analysis of these axes looks set to undermine this, says Dr Williams-Thorpe.

"One of the few archaeological arguments in favour of human transport to Stonehenge is that they were already making axeheads out of the same materials. But we happened to look at a few of these axeheads and found that half of them – three out of six – were not made of this bluestone.

"This is rather odd, because the literature says they are. But some rocks can look very similar when you pick them up in your hand; but when you start looking in detail and do a chemical analysis of them, they are actually different." The team's project is now to analyse all 30 or so reported "bluestone" axes and find out what they are actually made of.

Dr Williams-Thorpe herself favours the glaciation theory. "If people took the stones it was the largest and most difficult feat of stone transport we know of during the prehistoric period in Britain, possibly in Europe. There are about 900 stone circles in Britain, and only for Stonehenge is there any idea the stones were not obtained locally. They always came from within about four or five kilometres; indeed sometimes it is clear these monuments were built near the sources of stones on purpose."

The divisions between those favouring glaciation and those favouring human transport are deep. Dr Williams-Thorpe became embroiled more than 10 years ago when she and her late husband, Dr Richard Thorpe, together with John Watson and the late Dr Graham Jenkins, were given permission to analyse some of the Stonehenge monoliths. They came to the conclusion that they were not, as had been thought, from one single bluestone area, but from various sources as much as 20 kilometres apart. This, they argued, lent support to the glaciation theory.

The fierce argument unleashed by their findings, published in 1991, has made Dr Williams-Thorpe very wary of getting embroiled in the Stonehenge controversy again, she says. "People can disagree quite amicably about, say, the origins of the universe, but ask them whether they prefer glaciation or human transport for Stonehenge and they will get emotional, even personal.

"Our current research into axes will not solve the Stonehenge problem, but it does put a question mark over some of the evidence that has been quoted for 50 years.

"Probably the only way it could be finally resolved would be if we find a large bluestone glacial mass buried under Salisbury Plain. But there are good reasons to think there were only ever very few of them, so it is unlikely. If it does happen in my lifetime, I will be over the moon," she adds.