Largest ancient stone circle

Great Britain's largest megalithic prehistoric monument and largest henge are the 11.5ha (28.4 acre) earthworks and stone circles of Avebury, Wilts, `rediscovered' in 1646. The earliest calibrated date in the area of this Neolithic site is c.4200BC. The work is 365m 1200ft in diameter with a ditch 12m 40ft wide around the perimeter.