Stonehenge, which began to be built around 3000 BC, continues to mystify historians, archaeologists and geologists. The prehistoric stone circle is composed predominantly of locally-sourced sarsen (sandstone), but at its centre is a setting of smaller ‘bluestone’ monoliths. For these, spotted dolerite was used – an igneous rock that outcrops in West Wales, some 140 miles from Salisbury Plain.
How these bluestones first came to Stonehenge is subject to heated debate. The answer may come from recent discoveries of potential prehistoric quarries, where dolerite may have been extracted, in the Preseli Hills of Pembrokeshire. Yet some still contend that the bluestones were deposited on Salisbury Plain by glaciers.
Alternatively, the monoliths may originally have been part of a stone circle constructed in Wales, which was lifted and moved wholesale in the third millennium BC. But why the herculean effort to move such massive stones? It could be that the unusual spotted dolerite was prized by those living on the more colour-deficient chalk landscapes of Wiltshire.