Dear Sofia,
in his dialogue "Timaios", Plato conjectured that fire consists of little tetrahedrons (later it was conjectured that fire has something to do with a substance named "phlogiston"). He tries to find correspondences between the five regular (or "platonic") polyhedrons and the four elements. It leads him to some funny statements: for example, he claims that any triangle can be divided in a finite set of only two types of rectangular triangels, which is obviously untrue: for example, a regular fiveangle cannot be divided in a finite set of the two triangels Plato recommend. And he need the fiveangle to construct the dodekahedron, the fifth regular polyhedron, associated with a fifth element, the quintessence. Not his best book, I think, but the only book of him known in the middle age.

Yours,
John