A team of archaeologists and geologists working in Wales have found two of the quarries that provided stones for Stonehenge. The very large standing stones at Stonehenge are of ‘sarsen’, a local sandstone, but the smaller ones - known as ‘bluestones’ - come from the Preseli hills in Pembrokeshire. Geologists have known since the 1920s that the bluestones were brought to Stonehenge from somewhere in the distant Preseli Hills, but only now has there been collaboration with archaeologists to locate and excavate the actual quarries from which they came.
“This has been a wonderful opportunity for geologists and archaeologists to work together” said Mike Parker Pearson, director of the project and professor of British later prehistory at University College London. “The geologists have been able to lead us to the actual outcrops where Stonehenge’s stones were extracted.”
The Stonehenge bluestones are of volcanic and igneous rocks, the most common of which are called dolerite and rhyolite. Richard Bevins of the National Museum of Wales and Rob Ixer, honorary senior researcher at UCL and University of Leicester, have identified the outcrop of Carn Goedog as the main source of Stonehenge’s ‘spotted dolerite’ bluestones and the outcrop of Craig Rhos-y-felin as a source for one of the ‘rhyolite’ bluestones. Archaeological excavations at both sites have uncovered evidence of prehistoric quarrying.
The special formation of the rock, which forms natural pillars at these outcrops, allowed the prehistoric quarry-workers to detach each megalith (standing stone) with a minimum of effort. “They only had to insert wooden wedges into the cracks between the pillars and then let the Welsh rain do the rest by swelling the wood to ease each pillar off the rock face” said Dr Josh Pollard of the University of Southampton. “The quarry-workers then lowered the thin pillars onto platforms of earth and stone, a sort of ‘loading bay’ from where the huge stones could be dragged away along trackways leading out of each quarry.”
The team of scientists includes researchers from UCL, the universities of Manchester, Bournemouth and Southampton, the National Museum of Wales, and Dyfed Archaeological Trust. Professor Colin Richards of Manchester University, an expert in Neolithic quarries, said “The two outcrops are really impressive – they may well have had special significance for prehistoric people. When we saw them for the first time, we couldn’t believe our luck.”
Radiocarbon-dating of burnt hazelnuts and charcoal from the quarry-workers’ camp fires reveals that there were several occurrences of megalith-quarrying at these outcrops. Stonehenge was built during the Neolithic period, between 4,000 to 5,000 years ago. Both of the quarries in Preseli were exploited in the Neolithic, and Craig Rhos-y-felin was also quarried in the Bronze Age, around 4,000 years ago.
“We have dates of around 3400 BC for Craig Rhos-y-felin and 3200 BC for Carn Goedog, which is intriguing because the bluestones didn’t get put up at Stonehenge until around 2900 BC” said Parker Pearson. “It could have taken those Neolithic stone-draggers nearly 500 years to get them to Stonehenge, but that’s pretty improbable in my view. It’s more likely that the stones were first used in a local monument, somewhere near the quarries, that was then dismantled and dragged off to Wiltshire.”
Professor Kate Welham of Bournemouth University thinks that the ruins of any dismantled monument are likely to lie somewhere between the two megalith quarries: “We’ve been conducting geophysical surveys, trial excavations and aerial photographic analysis throughout the area and we think we have the most likely spot. The results are very promising - we may find something big in 2016.”
The megalith quarries are on the north side of the Preseli hills, and this location undermines previous theories about how the bluestones were transported from Wales to Stonehenge. Previous writers have often suggested that bluestones were taken southwards from the hills to Milford Haven and then floated on boats or rafts, but this now seems unlikely. “The only logical direction for the bluestones to go was to the north then either by sea around St David’s Head or eastwards overland through the valleys along the route that is now the A40” said Parker Pearson. “Personally I think that the overland route is more likely. Each of the 80 monoliths weighed less than 2 tons, so teams of people or oxen could have managed this. We know from examples in India and elsewhere in Asia that single stones this size can even be carried on wooden lattices by groups of 60 – they didn’t even have to drag them if they didn’t want to.”
Phil Bennett, archaeologist for the Pembrokeshire Coast National Park, said: “This project is making a wonderful contribution to our knowledge of the region’s importance in prehistory.” The new discoveries may also help to understand why Stonehenge was built. Parker Pearson and his team believe that the bluestones were erected at Stonehenge around 2900 BC, long before the giant sarsens were put up around 2500 BC. “Stonehenge was a Welsh monument from its very beginning. If we can find the original monument in Wales from which it was built, we will finally be able to solve the mystery of why Stonehenge was built and why some of its stones were brought so far”.
The project’s results are published this month in the journal Antiquity and in the January issues of British Archaeology and Current Archaeology. It also features in a new book published this month by the Council for British Archaeology, Stonehenge: making sense of a prehistoric mystery. Further excavations are planned for 2016.
The project is led by Prof. Mike Parker Pearson (UCL), Dr. Richard Bevins (National Museum of Wales), Dr. Rob Ixer (UCL and University of Leicester), Dr. Josh Pollard (University of Southampton), Prof. Colin Richards (University of Manchester), Mr. Duncan Schlee (Dyfed Archaeological Trust) and Prof. Kate Welham (Bournemouth University). It has been funded by the National Geographic Society, the Society of Antiquaries of London, the Royal Archaeological Institute, the National Museum of Wales and the Cambrian Archaeological Association, with support from the Pembrokeshire Coast National Park.