Theon (2) of *Smyrna (fl. c. 115–40 ce), Platonist (cf. plato(1)), author of an extant work, Aspects of Mathematics Useful for the Reading of Plato (Expos.), and of a lost commentary on the Republic. His treatise on the order of study of Plato's writings has recently been discovered in an Arabic translation. Aspects of Mathematics is an elementary work on arithmetic (especially on the types of numbers), the theory of musical harmony, and astronomy.