"Sometimes these huge stones were arranged in a circle known as a cromlech or henge , often surrounded by a ditch.  The most imposing today is Stonehenge on the Salisbury Plain in southern England.  Stonehenge is a complex of rough-cut sarsen (a form of sandstone) stones and smaller "bluestones" (various volcanic rocks). ... Stonehenge was probably built in several phases in the centuries before and after 2000 B.C."

- Gardner's Art Through The Ages, 11th edition, Vol. I, p. 15

Post-and-Lintel Construction, Stonehenge

"Outmost is a ring, almost one-hundred feet in diameter, of large monoliths of sarsen stones capped by lintels  (a stone 'beam' used to span an opening). Next is a ring of bluestones, which, in turn, encircle a horseshoe (open end facing east) of trilithons (three-stone constructions) - five lintel-topped pairs of the largest sarsens, each weighing forty-five to fifty tons."

- Gardner's Art Through The Ages, 11th edition, Vol. I, p. 15

Heel-Stone, Stonehenge

"Standing apart and to the east is the 'heel-stone," which, for a person looking outward from the center of the complex, would have marked the point where the sun rose at the midsummer solstice. ... Most archaeologists now consider Stonehenge a remarkably accurate solar calendar.  This achievement is testimony to the rapidly developing intellectual powers of Neolithic humans as well as their capacity for heroic physical effort."

- Gardner's Art Through The Ages, 11th edition, Vol. I, p. 15