Stonehenge: a transformative discovery

"Even by modern standards, John O'Groats to Wiltshire is a bit of a trek," said Hannah Devlin in The Guardian. Walking a solid eight hours a day, you might cover the nearly 500 miles in ten days – and that's without dragging a huge slab of stone behind you. So the revelation that Stonehenge's central altar stone – a six-tonne, five-metre-long rectangular piece of sandstone – arrived at the site around 4,500 years ago not from south Wales, as had previously been thought, but from the far northeast of Scotland, is, by any standards, astonishing.

X-ray analysis

The revelation appeared in an academic paper in Nature, written by six archaeologists and geologists from the UK and Australia, said Michael Le Page in New Scientist. It has long been known that Stonehenge's outer ring of larger stones ("sarsens") came from about 25km away in Wiltshire, and that nearly all the smaller "bluestones" that make up the inner circle came from the Preseli Hills in Pembrokeshire.

To identify the altar stone's source, they analysed a piece broken off in 1844 and kept in a museum (having used "X-ray fluorescence analysis" to confirm its authenticity). Then colleagues in Australia used methods developed in metals mining to analyse the fragments of stone: grains of zircon, apatite and rutile in the fragments all contain uranium, which slowly decays to lead, meaning they could be dated accurately. All this allowed the team to create a "fingerprint" of the mineral grains' source: it comes from sandstone of the Orcadian Basin, which stretches north from Inverness to Shetland.

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They wanted to 'make a point'

The science is "impressive" and the conclusion "clear cut", said Mike Pitts in The Spectator. But how did the monument's creators get the rock south? And why? The research team thinks that it was probably transported by sea, but my own view is that the overland route – using a vast sledge dragged by ropes – is more credible. Neolithic people didn't travel to their island's furthest extremity to get some sandstone because they had to: there was plenty much closer.

They did it, I believe, to "make a point". Journeying hundreds of miles let them spread the word about what they were building at Stonehenge, and connect with distant communities. "The longer the journey took, and the more people who gave their labour to the project, the more successful it was." The news about the altar stone's Scottish origins confirms that prehistoric Britain was home to complex societies, networked "in ways we are just beginning to understand". In my whole career as an archaeologist, I cannot remember a discovery about Stonehenge as transformative as this one.