DIOMEDES, Latin grammarian, flourished at the end of the 4th century A.D. He was the author of an extant Ars grammatica in three books. The third book is the most important, as contain ing extracts from Suetonius' De poetis. Diomedes wrote about the same time as Charisius (q.v.) and used the same sources in dependently. In book i. he treats of the eight parts of speech; in ii. of the elementary ideas of grammar and of style ; in iii. of quan tity and metres.