Stone circles and henges first appeared on the British Isles c. 3500 BCE, during the Neolithic period. Over 900 still exist today. Henges (oval shaped, banked ditches) enclosed ritual structures, such as stone circles, or villages, seen in excavations of the henge at Durrington Walls. The largest Neolithic structure in Britain is Marden Henge, close to Stonehenge. Discovered in 2015, its ramparts enclosed 15 hectares and excavations show that it was used as a gathering for feasts. It lacks the stone circles of other Neolithic sites, such as Stonehenge, Avebury, Beaghmore, and Bré na Bóinne (near Monknewtown) and archaeologists believe its standing stones may have been removed to farm the land. Stone circles differ, with recumbent stone circles specific to Ireland and Scotland, and characterized by a circle of standing stones that is constructed around a recumbent stone laid on its side. Concentric stone circles, typically found in England and Scotland, comprise two circles of standing stones arranged in a circular or oval configuration. Outlying stones, avenues and mounds may also form part of the site architecture and burials are found at concentric circle sites, indicating they played a part in funerary rituals. It is believed that stone circles were used for religious ceremonies, with entrances constructed to face sunrise and sunset or aligned with the sun during the winter or summer solstices.
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