Stonehenge is famous for its huge standing stones. The Altar Stone is counted among the bluestones, and its true home has changed part of the monument's story.
The way scientists solved the puzzle is as interesting as the answer. It came down to reading the ages of tiny grains inside the rock.
The Stone That Was Not From Wales
The Altar Stone is a block of sandstone, about 5 metres long and weighing about 6 tonnes.
Most of the other bluestones are known to come from the Preseli Hills in west Wales. The Altar Stone was long assumed to have come from Wales too.
A study published in Nature in August 2024 overturned that assumption. It concluded that the stone came from the Orcadian Basin in north-east Scotland. That region lies more than 700 kilometres from Stonehenge; the study gives a distance of about 750 km.
How Scientists Traced the Stone to Scotland
Rocks such as sandstone are made of small mineral grains that were once washed together. Some of those grains carry a kind of built-in clock, because their ages can be measured. Different regions have rocks with different mixes of grain ages, so the mix works like a fingerprint.
The 2024 study analysed tiny grains in the Altar Stone, including the minerals zircon, apatite and rutile. The team compared their ages with those in rocks from Scotland and Wales.
The work was led by researchers at Curtin University in Australia, including Anthony Clarke and Chris Kirkland, working with colleagues from other institutions in the UK.
The result was clear. The grain ages in the Altar Stone matched sandstones of the Old Red Sandstone type in the Orcadian Basin, and they did not match the Welsh rocks.
How We Know the Welsh Theory Failed
The evidence is set out in the August 2024 Nature paper, titled 'A Scottish provenance for the Altar Stone of Stonehenge'.
The Altar Stone is a sandstone, unlike the Preseli dolerite and rhyolite bluestones, which are other kinds of rock.
The study has a limit, too. It located the origin to a region of north-east Scotland, not to a single named quarry.
Why the Scottish Origin Matters
The result means a stone of about 6 tonnes was moved at least 700 kilometres. That is a much longer journey than any previously known for a Stonehenge stone.
Stonehenge's main stone circle was built around 2500 BC, in the late Neolithic and early Bronze Age.
The finding also points to links between communities across Neolithic Britain, from the north of Scotland to southern England.
