The oldest part of Stonehenge is a circular outer ditch believed to have been constructed before 2150 BC.
About 500 years later a double circle of 80 bluestones was erected. The stones are thought to have been brought from 200 miles away in southwest Wales, floated on rafts across the Bristol Channel, then dragged across Salisbury Plain.
Later the bluestones were taken down and replaced by two rings of sarsen (Saracen, or foreign) stones in the configuration that still stands.
Later still, some of the bluestones were re-erected. The largest, known as the Altar Stone, was set at the center of the monument and is still there. The entire edifice was probably completed around 1250 BC.
Controversy continues to surround the religious significance of Stonehenge.
Modern Druids insist that sun-worshiping ceremonies were common there four or five millennia ago. Others contest the belief that ancient Druids worshiped at Stonehenge, but concede that the site probably had religious and spiritual connotations.