Stonehenge’s altar stone was hauled from Scotland, not Wales

For generations, archaeologists have known that the stone at the heart of Stonehenge does not belong on Salisbury Plain in southern England.

Stonehenge on Salisbury Plain in southern England.

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For generations, archaeologists have known that the stone at the heart of Stonehenge does not belong on Salisbury Plain in southern England.

The six-tonne sandstone slab, known as the altar stone, lies at the centre of the prehistoric monument, but it is unlike the towering, locally sourced “sarsen” pillars that surround it. Since the 1920s scholars have guessed that it was imported from west Wales.

A new study appears to confirm a more distant origin and an even more exhausting journey for its hauliers: from the northeastern tip of Scotland.

The study, which involved blasting a fragment of the sandstone rock with a laser to record its chemical “fingerprint”, found that the altar is highly likely to come from the Orcadian Basin, a geological formation stretching from the southern Moray Firth to the Orkney and Shetland islands in the north. That implies it was transported at least 700km, probably about 4500 years ago – the longest known transit of a stone that size in the neolithic period.

“These findings are truly remarkable. They overturn what had been thought for the past century,” said Richard Bevins from Aberystwyth University, a co-author of the study. “It’s thrilling to know that our chemical analysis and dating work has finally unlocked this great mystery. We can now say that this iconic rock is Scottish and not Welsh.”

The research involved analysing mineral grains trapped inside the stone, which were shown to be between one billion and two billion years old, with other material found to have been created about 450 million years ago. This provided a distinct fingerprint, indicating an Orcadian origin.

It is not known how the stone was moved but in a study published in the journal Nature, the researchers write that a sea route seems likely, given the “difficulty of long-distance overland transport of such massive cargo from Scotland ... Such routing demonstrates a high level of societal organisation with intra-Britain transport.”

It was already known that the largest stones that make up Stonehenge - the sarsens, which are arranged in a horseshoe shape directly around the altar, and in a larger circle around the horseshoe - were hauled from about 25km away, from woodland just south of Marlborough in southern Wiltshire.

The “bluestones”, a collection of smaller pillars that now stand in a rough circle among the sarsens, are from further afield. In 1923 the geologist HH Thomas showed that most had been taken from the Preseli mountains of western Pembrokeshire. It was then widely assumed that the altar stone, which is the largest of the non-sarsen stones, came from the nearby shores of Milford Haven.

In 2020, scientists suggested a different source: near the inland town of Abergavenny, a few miles from what is now the English border. Last year scholars argued that the altar stone did not seem to be Welsh at all and speculated that it might have come from northern England or Scotland, a conclusion supported by the new paper.

The first major construction at Stonehenge was a circular ditch, with an internal bank and a smaller external bank, built in around 3000 BC. The sarsens and bluestones are thought to have followed roughly 500 years later. Today, the altar stone lies horizontal and is mostly buried beneath the fallen stone of what would have been the tallest sarsen trilithon (two vertical stones capped by a horizontal lintel).

What purpose it served is unknown, though at midwinter the sun would have set between the two uprights of the tallest trilithon, dropping down over the altar stone.

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