Little certain knowledge exists about Diomedes, author of an Ars grammatica dedicated to an unknown ‘Athanasius.’  He probably wrote for readers of the eastern empire (von Albrecht).  Since Rufinus cites him four times and Priscian cites him five, we may infer that he was active before the start of the 6^th c.  Determination of his terminus post quem depends on one’s interpretation of his relationship with Charisius, who - together with Donatus or Donatus’ models - represents Diomedes’ chief source: if the similarities between Diomedes and the work of Charisius arise from the direct influence of the latter, then Diomedes can probably be dated no earlier than 370-380 AD (thus Barwick); on the other hand, if their shared features derive from the use of a common source (the so-called “Charisius-Group”), then his relationship with Charisius is less certain, and his dating must necessarily be less precise (thus Mariotti, Ballaira, Mazhuga).  Kaster identifies certain turns of phrase in the prefatory epistle that, he argues, belong to the second half of the 4^th c. and find parallel in Symmachus; nevertheless, he does not find any formulae that are capable of resolving every difficulty.  According to Seng, the Cathemerinon of Prudentius reveals the influence of a theoretical and grammatical source very close to Diomedes; this would push his date to the second half or the end of the 4^th c. [A. Balbo; tr. C. L. Caterine].