National Geographic: Stonehenge Revealed

A Neolithic monument, Stonehenge has been used as a burial ground since its circular ditch and bank were cut into the chalk of Salisbury Plain about 3000 B.C. Other possible uses—a place of healing, a celestial observatory—remain hotly debated. Timber posts and pairs of four-ton bluestones were later set inside the circle near its center, along with an Altar Stone and Station Stones near the perimeter. Stonehenge took on its distinctive shape when Bronze-Age people added the 16-foot-high Sarsen Circle—30 stones capped with lintels. New earthworks were added, as was a banked roadway leading to the River Avon two miles away. Work at Stonehenge ended around 1500 B.C.