Attestation and identification. Bacchius is a figure known exclusively from Marcus's mention at 01-06. No other biographical data survives.

The most plausible prosopographical identification (Birley 2000, Hadot 1998, Farquharson 1944) is with Bacchius the Platonist, mentioned by Galen as a philosophical teacher of the Middle Platonist era. If this identification is correct, Bacchius belonged to the Middle Platonism of the second century — to the intellectual circle that included Gaius (Γάϊος), Albinus, Atticus, and others. This would account for his being listed first in the sequence of teachers under Diognetus: the introduction to philosophy in the second century often began from the Platonic dialogues as propaedeutic (which agrees with the fact that Marcus, on his own testimony at 01-06, himself began in these same years to write dialogues — a genre Platonic in origin).

The identification, however, remains open: the name Βάκχειος / Βάκχιος was widespread in the Hellenistic world, and without further data the coincidence may be accidental. Hard in the OWC commentary: "the identification is plausible but not provable." Farquharson: "we cannot be certain."

Alternative identifications rejected by the modern consensus. Gataker and Casaubon in the seventeenth century proposed identifying Bacchius with Eutychius Proculus — the Latin grammarian mentioned in SHA Marcus 2.3 as one of Marcus's early tutors. The proposal is rejected on two grounds: (a) Eutychius was a grammarian, not a philosopher, whereas Bacchius at 01-06 is embedded in a philosophical sequence (οἰκειωθῆναι φιλοσοφίᾳ); (b) the proposal requires an unmotivated emendation of the manuscript reading. More in 01-06, the correction to Rogovin's footnote ¹⁰.

Other possible bearers of the name (Bacchius the physician of Tanagra, the Hellenistic commentator on Hippocrates; Bacchius the music theorist) do not fit chronologically or by discipline.

• 01-06 — the sole mention.

• Galen, the mention of Bacchius the Platonist in the auto-bibliographical treatises (De libris propriis; De ordine librorum suorum) — if the identification is accepted.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000, ch. 3.
• A. S. L. Farquharson, The Meditations of the Emperor Marcus Antoninus, Oxford 1944, vol. II, ad 1.6.
• R. Hard, Marcus Aurelius: Meditations, OWC, Oxford 2011, notes ad 1.6.
• J. Dillon, The Middle Platonists, 80 BC to AD 220, Duckworth 1977 — the general context of the second-century Middle Platonism, within which Bacchius the Platonist would have been active.