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Sarsen – a distinctive form of sandstone that is found across southern England – seems to have been an important material for Neolithic monument-builders. It can be found in megalithic constructions in Kent, Oxfordshire, Dorset, and, most famously, Wiltshire. In this last county, unworked boulders form a key feature of Avebury’s c.4,500-year-old stone circles, while another huge piece of raw sarsen, known as the Heel Stone, can be seen just outside the main circuit of Stonehenge. As the latter monument demonstrates, though, Neolithic people were also capable of transforming this material into carefully shaped slabs. Precisely how this was achieved has long been the subject of debate, however, as sarsen (a particularly dense, hard stone) is challenging to work even with modern tools and technology.
William Gowland, a qualified mining engineer who excavated at Stonehenge in 1901, proposed a tripartite process involving splitting, flaking, and pecking boulders with the help of massive mauls. Gowland’s model was mainly based on contemporary ethnographic observations, but half a century later it was endorsed by Richard Atkinson (who led investigations at Stonehenge in the 1950s and 1960s), who added that wooden wedges might also have been involved. Now, Phil Harding of Wessex Archaeology has carried out a small practical project drawing on his decades of flint-knapping experience to explore what might have been possible for prehistoric stone-workers. His findings (recently published in The Antiquaries Journal and available open-access online; see ‘Further reading’ opposite), suggest an adaptation of techniques to work flint, using repeated blows on the same spot to build up shockwaves within the stone, is an effective way to split and shape sarsen.
Chipping away
Phil’s project has been a long time in the making. His initial interest in sarsen-working was sparked in 2008, during Geoff Wainwright and Tim Darvill’s excavation within the inner circle of Stonehenge (see CA 252), when Geoff asked if Phil was able to distinguish between sarsen flakes that had been struck off using a stone hammer and those from metal tools – that is, flakes linked to prehistoric construction and those reflecting later destruction such as Romano-British quarrying or post-medieval souvenir-hunting. Further inspiration came from discussions with colleagues about Wessex Archaeology’s investigations at MOD Durrington (completed in 2012), where finds included pieces of worked sarsen; and conversations about more recent research at Avebury.
Wanting to learn more about the working properties of sarsen, Phil devised his recently published project, during the course of which he compared the effectiveness of using a 454g (1lb) quartz pebble, a standard metal ball-pein hammer, and a 3kg (7lb) sledgehammer to split a 54kg (119lb) sarsen boulder. As well as consulting archaeologists, modern stonemasons, and engineers during his research, Phil also used his own extensive experience of working with another material that would have been very familiar to Neolithic communities: flint.
Flint and sarsen are both silicates, and if you put shockwaves through a silicate it will break. Flint responds to this process instantly, Phil explained – but while the much-harder sarsen requires more effort, he found that if you ‘stack up’ the shockwaves, hitting the exact same spot over and over again, the fracture plane will deepen and create a crack that widens until the stone splits cleanly in a predictable and controllable way, creating little in the way of waste. This control can be enhanced further by using a technique called point-loading, which involves placing a support underneath to make a linear pivot on which to snap the stone using repeated blows from above.
‘Control is very important,’ Phil said. ‘It doesn’t matter what material you are working with – if you can’t control it, you can’t do anything with it. It’s not just a case of just hitting the sarsen and expecting it to do what you want, you need to understand the material and how it breaks, understand the effect of shockwaves on silicates. Neolithic stoneworkers probably didn’t know what a silicate was, but they understood flint and they would have had at least a basic understanding that sarsen behaved like flint but was much harder, and that they could apply similar processes.’
Striking discoveries
Above all, Phil notes in his paper, his findings ‘indicate that direct percussion does provide a plausible technique for sarsen-working without having to stray beyond techniques and tools available to prehistoric communities.’ He adds: ‘The observed results add detail to Gowland’s “sledgehammering” technique. The repeated demonstration that a block of sarsen, approximately 0.2m thick, can be split in this way, using a 7lb (3kg) sledgehammer, suggests that the technique may be scaled up and applied effectively to fracture blocks approaching 1m thick, as represented by the Stonehenge monoliths and using mauls averaging 20kg in weight.’ As Gowland suggested, these mauls could have been made more effective with the addition of a handle, or the use of a tripod to create a drop-hammer effect. Phil also found that splitting created a clean, angular block that required very little supplementary trimming; flaking as a separate process provided no beneficial control over the stone.
As is the case with flint-knapping, the careful selection of materials would also have been vital for successful sarsen-working. Phil highlighted that while the Stonehenge uprights are impressively tall they are not particularly thick, perhaps indicating that the monument’s builders may have deliberately sought out large tabular slabs where they only had to trim down the edges. As for where suitable stones could be located, previous geochemical and statistical analysis shows that the most likely source for the Stonehenge sarsens is West Woods on the Marlborough Downs, about 30km (18.6 miles) north of the monument (CA 367). The fact that Neolithic people were willing to travel such distances and transport 20-tonne slabs back to Salisbury Plain suggests that there was something special about West Woods in a landscape where sarsen was plentiful.
The more clues that we glean about how Stonehenge may have been constructed, the more we appreciate the achievements of Neolithic communities working without modern technology. Even after identifying an effective technique, Phil notes: ‘sarsen remains fiendishly difficult to work.’
Further information: P Harding (2025) ‘Demystifying sarsen: breaking the unbreakable’, The Antiquaries Journal 105: 359-379; https://doi.org/10.1017/S0003581525100309.
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