Solids

A polyhedron is said to be regular if its faces are congruent regular polygons and if its polyhedral angles are all congruent. There is the tetrahedron with four triangular faces, the hexahedron, or cube, with six square faces, the octahedron with eight triangular faces, the dodecahedron with twelve pentagonal faces, and the icosahedron with twenty triangular faces. Plato mystically associates fire, earth, air, universe, and water to each regular solid.