towards the top in order that their perspective remains constant when viewed from the ground, while the lintel stones curve slightly to continue the circular appearance of the earlier monument. The inward-facing surfaces of the stones are smoother and more finely worked than the outer surfaces. The average thickness of the stones is and the average distance between them is . A total of 75 stones would have been needed to complete the circle (60 stones) and the trilithon horseshoe (15 stones). It was thought the ring might have been left incomplete, but an exceptionally dry summer in 2013 revealed patches of parched grass which may correspond to the location of missing sarsens. The lintel stones are each around long, wide and thick. The tops of the lintels are above the ground. Within this circle stood five trilithons of dressed sarsen stone arranged in a horseshoe shape across, with its open end facing northeast. These huge stones, ten uprights and five lintels, weigh up to 50 tons each. They were linked using complex jointing. They are arranged symmetrically. The smallest pair of trilithons were around tall, the next pair a little higher, and the largest, single trilithon in the south-west corner would have been tall. Only one upright from the Great Trilithon still stands, of which is visible and a further is below ground. The images of a 'dagger' and 14 'axeheads' have been carved on one of the sarsens, known as stone 53; further carvings of axeheads have been seen on the outer faces of stones 3, 4, and 5. The carvings are difficult to date but are morphologically similar to late Bronze Age weapons. Early 21st century laser scanning of the carvings supports this interpretation. The pair of trilithons in the north east are smallest, measuring around in height; the largest, which is in the south-west of the horseshoe, is almost tall. This ambitious phase has been radiocarbon dated to between 2600 and 2400 BC, slightly earlier than the Stonehenge Archer, discovered in the outer ditch of the monument in 1978, and the two sets of burials, known as the Amesbury Archer and the Boscombe Bowmen, discovered to the west. Analysis of animal teeth found away at Durrington Walls, thought by Parker Pearson to be the 'builders camp', suggests that, during some period between 2600 and 2400 BC, as many as 4,000 people gathered at the site for