Aristeides Quintilia'nus（Ἀριστείδης Κοϊντιλιανός), the author of a treatise in three books on music (Περὶ Μουσικῆς). Nothing is known of his history, nor is he mentioned by any ancient writer. But he must have lived after Cicero, whom he quotes (p. 70), and before Martianus Capella, who has made use of this treatise in his work De Nuptiis Philologiae et Mercurii, lib. 9. It seems probable also that he must be placed before Ptolemy, since he does not mention the difference between that writer and his predecessors with respect to the number of the modes. (Aristoxenus reckoned 13, his followers 15, but Ptolemy only 7. See Aristeid. pp. 22, 23; Ptol. Harm. 2.9.)
The work of Aristeides is perhaps the most valuable of all the ancient musical treatises.
It embraces, besides the theory of music (ἁρμονική) in the modern sense, the whole range of subjects comprehended under μουσική, which latter science contemplated not merely the regulation of sounds, but the harmonious disposition of everything in nature.
The first book treats of Harmonics and Rhythm; the former subject being considered under the usual heads of Sounds, Intervals, Systems, Genera, Modes, Transition, and Composition (μελοποιΐα).
The second, of the moral effects and educational powers of music; and the third of the numerical ratios which define musical intervals, and of their connexion with physical and moral science generally.
Περὶ Ποιητικῆς, which is lost. He makes no direct allusion to any of the ancient writers on music, except Aristoxenus.