Stonehenge, the most visited and well known of the British stone rings, is a composite structure built during three distinct periods. In Period I (radiocarbon-dated to 3100 BC), Stonehenge was a circular ditch with an internal bank. The circle, 320 feet in diameter, had a single entrance, 56 mysterious holes around its perimeter (with remains in them of human cremations), and a wooden sanctuary in the middle. The circle was aligned with the midsummer sunrise, the midwinter sunset, and the most southerly rising and northerly setting of the moon. Period II (2150 BC) saw the replacement of the wooden sanctuary with two circles of ‘bluestones’ (dolerite stone with a bluish tint), the widening of the entrance, the construction of an entrance avenue marked by parallel ditches aligned to the midsummer sunrise, and the erection, outside the circle, of the thirty-five ton ‘Heel Stone’. The eighty bluestones, some weighing as much as four tons, were transported from the Prescelly Mountains in Wales, 240 miles away.