Lying flat at the very center of Stonehenge, partially buried under two collapsed uprights, is a sandstone slab nearly five meters long and weighing six tonnes. It is not the most visually dramatic stone at the site. It does not catch the eye the way the trilithons do. But the Altar Stone has become, over the past two years, the most geologically disruptive object at the monument. Because it turns out to have come from the far north of Scotland, roughly 700 kilometers away, at a time when the landscape between its point of origin and Salisbury Plain looked nothing like it does today.
A new paper published in the Journal of Quaternary Science1 by Clarke, Veness, Kirkland, and colleagues takes that already remarkable fact and complicates it further. The question they are trying to answer is not just where the stone came from, but how, exactly, it got there. The answer they arrive at is partial, qualified, and in some ways stranger than either of the two leading hypotheses it was designed to test.
Those two hypotheses have been in competition for a while. One holds that Neolithic people moved the stone deliberately, hauling it overland or ferrying it by sea. The other proposes that a glacier did the heavy lifting, carrying the stone southward as an erratic during the last ice age, depositing it somewhere in England where it was later collected and installed. The glacier hypothesis is appealing because it offloads the most logistically implausible part of the problem onto natural forces. The human transport hypothesis is appealing because there is extensive evidence that Neolithic communities across Britain were capable of organizing exactly these kinds of long-distance movements. Neither hypothesis has been fully satisfying. The new paper explains why.
