Stonehenge, quite possibly the most famous archaeological site in the world, is a megalithic monument of 150 enormous stones set in a purposeful circular pattern, located on the Salisbury Plain of southern England, the main portion of it built about 2000 BC. The outside circle of Stonehenge includes 17 enormous upright trimmed stones of hard sandstone called sarsen; some paired with a lintel over the top. This circle is about 30 meters (100 feet) in diameter, and, stands about 5 meters (16 feet) tall.
Inside the circle are five more paired-and-linteled stones of sarsen, called trilithons, each of these weighing 50-60 tons and the tallest 7 meters (23 feet) high. Inside that, a few smaller stones of bluestone, quarried 200 kilometers away in the Preseli Mountains of western Wales, are set in two horseshoe patterns. Finally, one large block of Welsh sandstone marks the center of the monument.