Origin of Stonehenge’s Altar Stone
For over a century, archaeologists and historians operated under the firm belief that the massive Altar Stone sitting at the center of Stonehenge originated in Wales. However, a groundbreaking study published in August 2024 has completely rewritten this history. Advanced chemical analysis proves that this six-ton sandstone slab did not come from the Welsh hills, but from the Orcadian Basin in northeast Scotland, a staggering distance of roughly 466 miles (750 kilometers) away.
The Scientific Breakthrough
The discovery was led by Anthony Clarke, a PhD student at Curtin University, alongside researchers from Aberystwyth University, the University of Adelaide, and University College London. For decades, the Altar Stone was grouped with the “bluestones,” which are confirmed to have come from the Preseli Hills in west Wales.
To test this assumption, the team examined the age and chemistry of mineral grains within a fragment of the Altar Stone. They focused on zircon, apatite, and rutile grains. By using mass spectrometry to measure the ratio of uranium to lead in these microscopic crystals, they created a unique “age fingerprint” for the rock.
The results were definitive. The fingerprint did not match the geological profile of the Anglo-Welsh Basin. Instead, it was a direct match for the Old Red Sandstone found in the Orcadian Basin. This geological area encompasses parts of northeast mainland Scotland and the Orkney Islands.
The Logistics of a 466-Mile Journey
This finding creates a significant new mystery regarding Neolithic transportation. Stonehenge was built around 2600 BC. Moving a stone weighing six metric tons (over 13,000 pounds) from Scotland to the Salisbury Plain in southern England would have been a monumental task.
Researchers are currently analyzing two main theories regarding transport:
- The Overland Route: This would have involved dragging the stone across the rough terrain of the Pennines, through dense forests, and across treacherous bogs. Given the physical barriers and the sheer distance, experts believe this method would have been nearly impossible for the technology of the time.
- The Maritime Route: The more likely scenario is that the stone was transported by sea. This suggests that Neolithic people possessed advanced maritime skills and ships capable of carrying heavy cargo. They likely sailed the stone down the coast of Britain before transporting it inland to the construction site.
Implications for Neolithic Society
The Scottish origin of the Altar Stone suggests that the island of Great Britain was much more connected in the Neolithic era than previously thought. This was not a localized construction project. It appears there was a high level of societal organization and coordination between distinct communities separated by hundreds of miles.
The Orcadian Basin, particularly the Orkney Islands, was a major cultural hub during the Neolithic period. It is home to other significant monuments like the Ring of Brodgar and Skara Brae. The transport of the Altar Stone suggests a direct link or alliance between the people of the Orkney region and the builders of Stonehenge in the south.
Understanding the "Fingerprint" Analysis
The science used to identify the stone’s origin relies on the durability of zircon crystals. Zircon is incredibly resilient to heat and pressure, meaning it retains its chemical composition for billions of years. It acts as a time capsule for geologists.
When the sandstone formed, it incorporated eroded grains from older rocks. By dating these grains, the researchers found that the Altar Stone contains minerals that are roughly 1 billion to 2 billion years old. This specific age range is characteristic of Scottish geology. In contrast, the rocks in Wales generally contain minerals from different geological eras, making the distinction clear once the chemical analysis was complete.
Frequently Asked Questions
What is the Altar Stone? The Altar Stone is a large, flat block of sandstone lying at the center of the Stonehenge stone circle. It is distinct from the upright sarsen stones and the smaller bluestones. It weighs approximately six tons and is partially buried.
Why did researchers think it was from Wales? In 1923, geologist Herbert Thomas suggested the Altar Stone came from the same area as the bluestones (the Preseli Hills in Wales). Because both were “foreign” stones (not local to Salisbury), it was assumed they were transported together. This theory went largely unchallenged until recent chemical tests proved it wrong.
How long did the journey take? While we do not know the exact duration, a sea voyage from northeast Scotland to southern England in Neolithic vessels would likely have taken several weeks, depending on weather and stops.
Does this change the age of Stonehenge? No, this discovery does not change the dating of the monument itself, which was constructed in phases between 3000 BC and 2000 BC. However, it radically changes our understanding of the resources and networks available to the people who built it.