Triglyph means "three [tri] mark [glyph]" --and indeed triglyphs on the facade of a Doric style temple are raised rectangular areas, each of which have three vertical marks. The archeological evidence is that this traditional form originated in the ceramic caps that the Greek architects fastened to the exposed ends of wooden beams that rested on the architrave. The end of a beam is the part most vulnerable to rot, so these early triglyphs were intended to prolong the life of the beams. Later, this traditional form was translated into stone.