TRILITHON

A 'trilithon' (or ''trilith'') is a structure consisting of two large vertical stones supporting a third stone set horizontally across the top. Commonly used in the context of megalithic monuments. the most famous trilithons are those at Stonehenge and those found in the prehistoric temples in Malta, which are a UNESCO World Heritage Site.
The word ''trilithon'' is derived from the Greek 'having three stones' ('Tri' - ''three'', 'lithos' - ''stone'') and was first used by William Stukeley.
The term also describes the groups of three stones in the Hunebed tombs of the Netherlands and the three massive stones forming part of the wall of the Roman Temple of Jupiter at Baalbek, Lebanon.