A trilithon (or trilith) is a structure consisting of two large vertical stones (posts) supporting a third stone set horizontally across the top (lintel). It is commonly used in the context of megalithic monuments. The most famous trilithons are those of Stonehenge in England, those found in the Megalithic temples of Malta—both of which are UNESCO World Heritage Sites—and the Osireion in Egypt. The word trilithon is derived from the Greek "having three stones" (τρι-/tri- 'three' + λίθος/lithos 'stone') and was first used by William Stukeley.