The best-known of all megalithic sites, the circle at Stonehenge dates back 4000 years; the tallest upright stone is 22-ft-tall. The outermost element of the site is the Avenue, running straight down into Stonehenge Bottom and the Heel Stone, a large upright unworked sarsen (hard sandstone). It is known that there were at least two entrances, the one now visible, and one to the south. Lying within the entrance is an unworked and now recumbent sarsen stone, stained a rusty red (caused by rainwater acting on iron), and known as the Slaughter Stone. Arranged around the inner edge of the earthwork bank were originally four small uprights known as the Station Stones; two are still visible. Immediately adjacent to the bank is a ring of 56 pits, known as the Aubrey Holes. On the central area of the site are the stone settings, the sophisticated arrangements that set Stonehenge apart from any other prehistoric monument in Europe.
