Diomedes Grammaticus was a Latin grammarian who probably lived in the late 4th century AD.
He wrote a grammatical treatise, known either as De Oratione et Partibus Orationis et Vario Genere Metrorum libri III or Ars grammatica in three books, dedicated to a certain Athanasius.
This book contains one of the most complete lists of types of dactylic hexameters in antiquity, including the teres versus, which may (or may not) be the so-called "golden line."
The works of both grammarians are valuable, but whereas much of Charisius has been lost, the Ars of Diomedes has come down to us complete (although probably abridged).
In book I he discusses the eight parts of speech; in II the elementary ideas of grammar and of style; in III poetry, quantity, and meters.