Literally a large stone. The practice of building with large stones occurred in such diverse places as Inca Peru, ancient Egypt, and Easter Island. Megaliths usually consist of blocks built into tombs and other monuments in western Europe in the Neolithic to Bronze Age, c.4000–1500 bc. They were once thought to have been derived from a single source, but further study and close dating suggest that that is too simple a view, and that many areas were involved.

While many monuments consist of separate stones raised on end as menhirs, stone circles (as at Stonehenge), and avenues (as seen at Carnac, in France), the same technique was often used in walling chambers. Roofs could be of horizontal capstones to make the so-called dolmens, or of oversailing courses of slabs, which are known as corbelled vaults. The largest block recorded is the capstone of the tomb at Browneshill, County Carlow, Ireland, estimated to weigh 100 tonnes. The movement, handling and dressing of such large stones, and, in some cases, their precise orientation, indicate that those responsible had considerable skill in mechanics, mathematics, and the organization of labour.