Stonehenge's huge blocks DID arrive over land as archaeologists debunk theory the Neolithic slabs were rafted from Wales to Salisbury Plain
- The Neolithic monument is made of both locally and distant-sourced stones
- The 'Altar Stone' has long been linked to Milford Haven, in Pembrokeshire
- This led to the theory that the stones travelled by sea and up the Bristol Channel
- Fresh analysis found that the Altar Stone does not match the Milford Haven rocks
- There is thus now 'no scientific evidence' to support the raft theory, experts said
- Instead, it seems more likely that the stones travelled a route similar to the A40
Stonehenge's bluestone blocks did arrive over land, archaeologists have concluded — debunking a theory that the giant slabs were rafted from Wales to Salisbury Plain.
It has long been known that the famous Neolithic monument is made up both of local stones and some sourced from much further away, in Wales' Preseli Hills.
The debate over which path these rocks took to Stonehenge has long been anchored by a unique block called the 'Altar Stone', thought collected en-route.
A popular theory had suggested the Altar Stone came from the Pembrokeshire coast, at Milford Haven, with the blocks then sailed up the Bristol Channel.
However, a new analysis of the age and mineral composition of both the Altar Stone and its supposed source revealed that the two do not actually match.
Instead, the Altar Stone is likely to have come from further east — near the modern-day town of Abergavenny — suggesting the bluestones were transported by land.
In fact, the stones may have followed a route quite similar to the A40 trunk road that connects Wales with London today.
Stonehenge's bluestone blocks did arrive over land, archaeologists have concluded — debunking a theory that the giant slabs were rafted from Wales to Salisbury Plain, pictured. It has long been known that the monument is made up both of local stones and some sourced from Wales' Preseli Hills. The debate over which path these rocks took to Stonehenge has long been anchored by a unique block called the 'Altar Stone', thought collected en-route
A popular theory suggested the Altar Stone came from the Pembrokeshire coast, at Milford Haven, with the blocks then sailed up the Bristol Channel. However, a new analysis of the age and mineral composition of both the Altar Stone and its supposed source revealed that the two do not actually match. Instead, the Altar Stone is likely to have come from further east — near the modern-day town of Abergavenny — suggesting the bluestones were transported by land
Built around 3,000–2,000 BC, Stonehenge contains various groupings of rock — the green-grey 'sarsens', the so-called 'bluestones' and the purplish-green 'Altar Stone'.
The sandstone sarsens — Stonehenge's most prominent slabs — were sourced locally, from Marlborough Downs, a mere 20 miles from the site of the monument.
Less obvious, however, is the provenance of the so-called 'bluestones' — a loose term used to refer to all the non-local rocks that make up the rest of the monument.
These are mainly made up of relatively small blocks of the igneous rocks 'dolerite' and 'rhyolite' — but also includes the so-called 'Altar Stone', which is distinct.
Made of a geologically younger, mica-rich sandstone, the Altar Stone — or 'Stone 80' — is a flat-lying, 6.5 feet (2 metres)-wide block thought to weight around six tons, currently partially hidden under two fallen sarsen stones.
The first detailed analysis of the bluestones was undertaken by the British geologist and archaeologist Herbert Henry Thomas in 1923, who linked most of the stones with rocks found some 150 miles away in the Preseli Hills of north Pembrokeshire, Wales.
In contrast, Dr Thomas suggested that the Altar Stone matched two outcrops of similar rock found further to the south.
The first was the so-called 'Senni Formation' — which can be found between Kidwelly and Abergavenny in South Wales — and the second was the so-called 'Cosheston Subgroup', found on the shores of Milford Haven, in Pembrokeshire.
The notion that the Altar Stone came from Milford Haven had a profound influence on theories as to how the bluestones were transported to Stonehenge — with the idea being that the Altar Stone may have been collected en-route.
Many experts accordingly suggested that, from Milford Haven, the bluestones and the Altar Stone were shipped on rafts up the Bristol Channel, before travelling the final leg to Salisbury Plain over land.
The theory had proven so popular, in fact, that a number of attempts have been made since to re-enact the journey.
Recent studies, however, have called into question the original connection between the Altar Stone and the sandstone outcrops in South Wales and Pembrokeshire — and similarly challenge the notion the blocks travelled by sea from Milford Haven.
Some researchers have even concluded that the bluestones came from the northern flanks of the Preseli Hills — meaning that, to go via Milford Haven and the sea, they would first have to have been tortuously hauled all the way over the hills.
Made of a geologically younger, mica-rich sandstone, the Altar Stone — or 'Stone 80' — is a flat-lying, 6.5 feet (2 metres)-wide block thought to weight around six tons, currently partially hidden under two fallen sarsen stones, pictured
Built around 3,000–2,000 BC, Stonehenge contains various groupings of rock — the green-grey 'sarsens', the so-called 'bluestones' and the purplish-green 'Altar Stone' (shown in red)
The sandstone sarsens — Stonehenge's most prominent slabs — were sourced locally, from Marlborough Downs, a mere 20 miles from the site of the monument. Less obvious, however, is the provenance of the so-called 'bluestones' — a loose term used to refer to all the non-local rocks that make up the rest of the monument. Pictured, Stonehenge as viewed from above
In their new study, archaeologist Rob Ixer of the University College London and colleagues re-examined both the Altar Stone and the sandstones of the Cosheston Subgroup, its proposed source in Milford Haven.
The team used advance X-ray spectroscopy techniques to determine the exact mineral make-up of both rocks — and measured the isotope ratios of tiny crystals of zircon to determine how old each sandstone was.
The results, the researchers said, 'show that the Altar Stone could not have come from the sandstones exposed at Milford Haven.
'Its mineralogy and zircon age profile are very different.'
With the Altar Stone now revealed to have not come from Milford Haven at all, the team explained, there is now 'no scientific evidence' for the idea that the bluestones were transported southward to there from the Preseli Hills, and on by sea, at all.
‘This totally destroys the raft theory. It blows it out of the water,' added Dr Ixer.
‘This is our second re-examination of the bluestones, but it is our first major finding.’
The findings, the researchers said, 'show that the Altar Stone could not have come from the sandstones exposed at Milford Haven. 'Its mineralogy and zircon age profile are very different.' Pictured, false colour particle maps showing the minerals making up the Altar Stone (top) and a sample of sandstone from Milton Haven (bottom). On a microscopic scale, they are distinct
Dr Thomas had originally suggested that the Altar Stone matched two outcrops of similar rock found further to the south. The first was the so-called 'Senni Formation' (shown in orange) — which can be found between Kidwelly and Abergavenny in South Wales — and the second was the so-called 'Cosheston Subgroup' (green), found on the shores of Milford Haven, in Pembrokeshire. Pictured, a geological map of southern Wales
'The quest is now to find the real source of the Altar Stone. We can exclude areas in West Wales as there are no suitable geological sources,' the researchers said.
One possibility is that Dr Thomas' other suggestion — that the Altar Stone came from the Senni Formation of the Abergavenny area, near the English border — was closer to the mark.
'This eastern section of the Senni Formation lies on a natural routeway leading from west Wales to the Severn estuary and beyond,' the researchers wrote.
'Followed today by the A40 road, its route along the valleys may well have been significant in prehistory, raising the possibility that the Altar Stone was added to the assemblage of Preseli bluestones taken to Stonehenge around [...] 3000 BC.'
In this theory, the bluestones from the Preseli hills would have been transported past Abergavenny — where the Altar Stone was collected — before crossing the Severn River near Gloucester and then heading south-east to Salisbury Plain.
To fix the exact route the bluestones took, however, the precise source of the Altar Stone will still need to be located, the researchers cautioned.
'When the source is located, the implications for transport routes can be explored,' they added.
The full findings of the study were published in the Journal of Archaeological Science.
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