LONDON — Stonehenge is believed to have been completed around 1250 BC. The oldest part is a circular outer ditch constructed before 2150 B.C.
About 500 years later, a double circle of bluestones was erected. The stones were brought from the Prescelly Hills, 200 miles away in southwest Wales, floated on rafts across the Bristol Channel, then dragged overland to their present position.
Later, for unknown reasons, the bluestones were taken down and replaced by two rings of sarsen (that is, Saracen, or foreign) stones in the present configuration. The stones came from nearby Marlborough Downs. Later still, some of the bluestones were put up again. The largest, known as the Altar Stone, was set at the very center of the monument and is still there.
About 100 yards away is the Heelstone. The sun rises over the top of this stone every June 21, the longest day of the year.
Visitors' fascination with Stonehenge is prompted partly by the sheer magnitude of the effort that created it. It is scarcely possible to look at it without sharing the physical burden of the people who lugged such heavy pieces of rock to the site and erected them with such geometric precision.
But an air of mystery about the religious and spiritual significance of Stonehenge adds to the fascination. Arguments among experts - real and self-proclaimed - abound.
Modern Druids say that sun-worshipping ceremonies were common there 4,000 or 5,000 years ago. Others deny that ancient Druids worshiped at Stonehenge but accept that the site probably had religious connotations.
In recent years, Stonehenge has attracted hippie groups who antagonized local residents. A few years ago, a visitor carved an anarchist symbol into one of the stones. Self-styled Druids who arrive at Stonehenge and hope to observe the summer solstice from close to the ring of stones are now frustrated: Police prevent them from entering a four-mile exclusion zone.