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Stonehenge is a prehistoric monument in Wiltshire, England, 2 miles (3 km) west of Amesbury.
It consists of a ring of standing stones, with each standing stone around 13 feet (4.0 m) high, 7 feet (2.1 m) wide and weighing around 25 tons.
The surrounding circular earth bank and ditch, which constitute the earliest phase of the monument, have been dated to about 3100 BC.
Radiocarbon dating suggests that the first bluestones were raised between 24 BC, It has been a legally protected Scheduled Ancient Monument since 1882 when legislation to protect historic monuments was first successfully introduced in Britain.
Archaeologists have found four, or possibly five, large Mesolithic postholes (one may have been a natural tree throw), which date to around 8000 BC, beneath the nearby modern tourist car-park.
These held pine posts around 0.75 metres (2 ft 6 in) in diameter, which were erected and eventually rotted in situ.
Salisbury Plain was then still wooded but 4,000 years later, during the earlier Neolithic, people built a causewayed enclosure at Robin Hood's Ball and long barrow tombs in the surrounding landscape.
The Oxford English Dictionary cites Ælfric's tenth-century glossary, in which henge-cliff is given the meaning "precipice", or stone, thus the stanenges or Stanheng "not far from Salisbury" recorded by eleventh-century writers are "supported stones".
William Stukeley in 1740 notes, "Pendulous rocks are now called henges in Yorkshire...
Three of the posts (and possibly four) were in an east-west alignment which may have had ritual significance.
Another Mesolithic astronomical site in Britain is the Warren Field site in Aberdeenshire, which is considered the world's oldest Lunar calendar, corrected yearly by observing the midwinter solstice.
In approximately 3500 BC, a Stonehenge Cursus was built 700 metres (2,300 ft) north of the site as the first farmers began to clear the trees and develop the area.