The bluestones at Stonehenge are the smaller rocks you can see standing inside the huge sarsens that form the outer circle and the inner trilithons.
They range in size from stumps barely visible in the turf through to slender pillars standing nearly 2.5m tall (plus another metre or more below gound) with the largest weighing between 2 and 3 tonnes.
These rocks definitely come from the Preseli Mountains in southwest Wales, 150 miles from Stonehenge as the crow flies. Their place of origin was first established in 1923 by the geologist H. H. Thomas and has been confirmed by modern geochemical analysis. They used to be known as the “foreign stones” because it was recognised that they weren’t local to the Stonehenge area.
The name bluestone is a collective term and there are two main types – spotted dolerite and rhyolite.
It’s not obvious why they’re called bluestones to most people since at first glance, and especially from a distance, they look more greyish green in colour. But a freshly broken piece of the dolerite type reveals that the unweathered interior is a striking blue-green colour with white spots.
How and – more importantly – when and why they were brought to Stonehenge is a matter of lively debate.
Being comparatively lightweight, the transportation from Preseli to Stonehenge may have been accomplished fairly simply despite the distance involved. In the 1950s a team of a few dozen teenage schoolchildren was easily able to drag a replica bluestone using rollers and a sledge, and half a dozen were able to pilot one on a raft up and down a small river with no trouble.
One theory of when they arrived at Stonehenge suggests that it was around 3000BC and that they were placed in a circle just inside the earthwork bank in the 56 sockets that are known as the Aubrey Holes. This was 500 years before the large sarsens were put up. Subsequently, this theory says, they were moved to within the sarsen monument and re-arranged at least twice.
The question of why anyone would go to the bother of transporting up to 80 rocks from Wales to Wiltshire is unanswerable. It may be that they formed an existing monument that was dismantled as the spoils of war, they might represent the ancestors of a group of people who migrated eastwards or they may even have been a gift from one population to another.
They clearly had some great significance, perhaps because of their striking position in easily quarried outcrops on the top of the Preseli Mountains.
Curiously, a number of the Stonehenge bluestones were once the components of two bluestone trilithons that must have stood about 2.5m tall. The evidence is in the form of two half-buried bluestone lintels that have mortise holes worked into them and several other standing bluestones that have the remains of tenons on their tops.
These individual components are now placed remotely from each other at Stonehenge but perhaps these small trilithons were the inspiration for the enormous sarsen versions that still stand at the monument.
There are only about 30 visible bluestones remaining at Stonehenge and it is likely that the others have been chipped to pieces for souvenirs and talismen or stolen away for use elsewhere in the last 5000 years. Local rumours of bluestone doorsteps, bridge footings and magnificent fireplaces crop up every so often and fragments have been found in many of the nearby Bronze Age burial mounds. Stonehenge special access tours allow you to enter the inner circle of Stonehenge and get close to the blusestones.
Article by guest blogger and local Stonehenge historian Simon Banton