Megalith, a monument made of huge, roughly hewn stone slabs erected by Stone Age or Bronze Age people. An individual stone slab that is part of a monument is also called a megalith. Megalithic monuments are found in many parts of the world, but the largest number are found in western Europe.

A single, tall stone in an upright position is known as a menhir. A row of menhirs is called an alignment, or avenue. A circle of menhirs is sometimes called a stone circle, or cromlech. Standing stones capped by a flat stone form a dolmen. Many ancient barrows (burial chambers) are dolmens covered with earth.

Wiltshire, in southern England, contains many megalithic structures, the most notable of which is Stonehenge, near Salisbury. A 28 1/2 acre (11.5-hectare) site at Avebury has several stone circles and alignments of menhirs. Stones arranged to form a giant cross with a center circle stand at Callanish, on Lewis Island of the Outer Hebrides. At Carnac, on the Brittany coast of France, are long alignments of more than 2,000 menhirs. Ireland and Corsica also have notable megalithic remains.

picture titled Dolmen in County Clare; Stonehenge.