The five Platonic solids, also known as the five regular solids, were discovered in ancient times. Although each one was probably known prior to 500 BC, they are collectively named after the ancient Greek philosopher Plato (428-348 BC) who mentions them in his dialogue Timaeus, written circa 360 BC. Each Platonic solid uses the same regular polygon for each face, with the same number of faces meeting at each vertex. The five Platonic solids are the only convex polyhedra that meet these criteria.