Stonehenge, group of standing stones on Salisbury Plain, Wiltshire, S England. Preeminent among megalithic monuments in the British Isles, it is similar to an older and larger monument at Avebury. The great prehistoric structure is enclosed within a circular ditch 300 ft (91 m) in diameter, with a bank on the inner side, and is approached by a broad roadway called the Avenue. Within the circular trench the stones are arranged in four series: The outermost is a circle of sandstones about 13.5 ft (4.1 m) high connected by lintels; the second is a circle of bluestone menhirs; the third is horseshoe shaped; the innermost, ovoid. Within the ovoid lies the Altar Stone. The Heelstone is a great upright stone in the Avenue, northeast of the circle.

It was at one time widely believed that Stonehenge was a druid temple, but this is contradicted by the fact that the druids probably did not arrive in Britain until c.250 B.C. In 1963 the American astronomer Gerald Hawkins theorized that Stonehenge was used as a huge astronomical instrument that could accurately measure solar and lunar movements as well as eclipses. Hawkins used a computer to test his calculations and found definite correlations between his figures and the solar and lunar positions in 1500 B.C. (However, as a result of the development of calibration curves for radiocarbon dates, Stonehenge is now believed to have been built in several stages between c.3000 and c.1500 B.C., with the main construction completed before 2000 B.C.) Some archaeologists objected to Hawkins's theory on the basis that the eclipse prediction system he proposed was much too complex for the Early Bronze Age society of England.

Most archaeologists agree, however, that Stonehenge was used to observe the motions of the moon as well as the sun. Research by the archaeologist Alexander Thom, based on the careful mapping of hundreds of megalithic sites, indicates that the megalithic ritual circles were built with a high degree of accuracy, requiring considerable mathematical and geometric sophistication. More recent speculation on the Neolithic ceremonial and cultural functions of Stonehenge has included its possible use as a center for healing and as a burial ground for a local ruling family.

Monumental circular arrangement of standing stones built in prehistoric times and located near Salisbury, Wiltshire, Eng. The stones are believed to have been put in place in three main phases circa 3100–circa 1550 BC. The reasons for the building of Stonehenge are unknown, but it is believed to have been a place of worship and ritual. Many theories have been advanced as to its specific purpose (e.g., for the prediction of eclipses), but none has been proved. Stones erected during the second phase of construction (circa 2100 BC) were aligned with the sunrise at the summer solstice, suggesting some ritual connection with that event.

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