In the Timaeus (circa 355-347 B.C.E.); Plato uses the geometrical shape of each element to explain its appearance and behavior:

First, let us ask what we mean when we say that fire is hot. We get a clue from the divisive and cutting effect it has on our bodies. We all feel that fire is sharp, and we should also consider the sharpness of the sides[of the four triangles that compose fire]. . .which make fire cut whatever it touches. We should also remember that the original [pyramidal] shape of fire, more than any other form, has a divisive ability to cut our body into small pieces. This naturally causes the sensation called heat . . .

We give earth the form of a cube, since earth is the most immovable of the four elements and the most malleable of all...