The Greeks proposed the existence of five basic elements. Of these, four were the physical elements – Fire, Air, Water and Earth – of which the entire world is composed. Alchemists eventually associated four triangular symbols to represent these elements.
– Elemental-Symbols, Catherine Beyey, About.com, Altreligion.about.cm (http://altreligion.about.com/od/westernocculttradition/ig/Elemental-Symbols/)