The Bluestones of Stonehenge

The stone circles of Stonehenge are built from two main types of rock. The massive sarsens that are a sandstone, and a variety of smaller igneous rocks known as the bluestones. It has been known since the 16th century that the sarsen stones came from near to Marlborough, 30 km north of Stonehenge.
It was only 350 years later that the source of the bluestones was pinpointed. The three main types of bluestone come from the Preseli Hills in north Pembrokeshire. On Carn Menyn some of the stones could simply have been collected from the surface.
It has been argued that the stones were transported from Wales by glaciers. However, comprehensive geological studies have shown that there is no evidence for a glaciation in Wessex that could have transported these rocks and left no other trace.
When the stones were transported to Stonehenge and added to the temple that already stood there is less easy to establish. The stones helped to transform the layout of the monument so that it was aligned on the sunrise on the longest day of the year; and sunset on the shortest day.
The bluestone settings at Stonehenge are thought to have been re-arranged at least four times within a period about 400 years between 2,400 and 2,000 BC. There may have been plans for a fifth arrangement that was not completed.
The date at which the bluestones first arrived at Stonehenge is not known. It can only be said that the first bluestone setting (Phase 3i: the Q and R holes) is earlier than the completion of the setting of great sarsen stones, which is radiocarbon dated to 2,440-2,100. Pieces of beaker pottery found in the backfill of one of the stoneholes of this first bluestone setting show that Beaker pottery was in use when that stone was removed.
It is not known whether all the bluestones arrived at the same time. Richard Atkinson, who with Stuart Piggott, was the most recent excavator at Stonehenge, favoured this option. But Ros Cleal, Karen Walker and Becky Montague who published those excavations, preferred to see the bluestones as having arrived in two major episodes. The second episode being after the sarsen settings had been erected and when the Bluestone Circle and Bluestone Oval were built. The Bluestone Circle is radiocarbon dated 2,280-2,030.