Scarcity of sources. Cinna Catulus is a figure to be reconstructed biographically only minimally. Everything we securely know about him is exhausted by:

1. The mention in Marcus's catalogue of mentors (01-13) — the only developed testimony, and even this reports only the ethical "receipt," not biographical data.
2. Inclusion in the standard list of Marcus's philosophical teachers in SHA Marcus (Vita Marci, ch. 3), where Catulus is named among the Stoic mentors alongside Apollonius of Chalcedon, Junius Rusticus, Sextus of Chaeronea, Claudius Maximus, and others.

Beyond these two testimonies, no biographical details, no anecdotes, no surviving fragments of writings. The prosopographical handbooks (PIR², prosopographical databases of Roman philosophers) give him a short entry primarily on the basis of these same two sources, without adding reliable information. In Rogovin's footnote to 01-13 he is called "Cinna Catulus," and this form of the name is standard in current academic usage.

School affiliation. Stoic. This is known both from the SHA (where Catulus is directly classified among the Stoic teachers) and indirectly from Med. 1.13 itself: the content of Marcus's thanks (on τέκνα ἀγαπητικόν, on φίλος αἰτιώμενος, on ἐκθύμως εὔφημον περὶ τῶν διδασκάλων) reproduces the general Stoic ethics of σχέσεις and philostorgia, with none of the characteristic Platonic or Peripatetic colourings.

Contrast with the other Stoic mentors. Among the Stoics of Book I, Rusticus (01-07), Apollonius (01-08), and Sextus (01-09) have an external biographical accretion — career data, anecdotes, mentions in Lucian, in Philostratus, in Aulus Gellius, in the SHA Pius. Catulus has no such accretion: no anecdotes about him survive, no mentions in non-philosophical literature of the second century. Marcus mentions him only once, and that entry is the only "portrait" of Catulus available to us. In this respect Catulus is the most "internal" teacher of Book I: he exists for us solely through Marcus's thanksgiving, without external witnesses.

Educational role

A threefold ethical thanksgiving. Med. 1.13 is formally the only entry of Book I in which Marcus addresses three discrete ethical lessons to a single teacher, with no reduction to a single thesis. These are what Catulus transmitted to Marcus:

1. Not to disregard a friend's complaint, even an unreasonable one, but to try to restore the relation to its customary state (ἀποκαθιστάναι ἐπὶ τὸ σύνηθες). Friendship as a relational fact, not as a contract on the merits.
2. To speak well of teachers from the heart (ἐκθύμως εὔφημον περὶ τῶν διδασκάλων), on the model of one Domitius and Athenodotus (figures, as Rogovin's footnote to 01-13 notes, unknown to us).
3. To love children truly (ἀληθινῶς ἀγαπητικόν), without the formal mask of parental attachment.

A generic peculiarity of the portrait. Unlike the teachers whose names are fixed to a single programmatic trait (for example, Rusticus for the transmission of Epictetus's Discourses; Apollonius for the sustained ἀπάθεια in the face of pain and bereavement; Fronto for the observation of the tyrannical triad), Catulus is preserved in Marcus as a composite portrait: a teacher from whom Marcus took several local norms relating to different spheres of the close circle (friends / teachers / children). This perhaps also explains the thinness of his biographical trace: Catulus is remembered as a sum of lessons, and each lesson individually is sufficiently common that it does not require an outstanding biographical persona.

The Stoic background of the three lessons. All three lessons locally reproduce the general Stoic doctrine of σχέσεις (relations) and καθήκοντα (appropriate actions), in the version systematically developed by Epictetus (see Disc. 2.10 — discussed in the commentary to 01-12). Friend, teacher, child — all three are σχέσεις in Epictetus's sense: social roles from which specific καθήκοντα follow. Catulus was apparently a Stoic of an ethico-practical cast, oriented toward the working-out of these relational obligations in their everyday granularity, rather than toward doctrinal courses on physics or logic.

• 01-13 — the only direct and the only developed mention; the source of everything we know about Catulus as a teacher.
• 01-17 — the thanksgiving to the gods for "having received good teachers"; Catulus is implicitly among them.

• SHA Marcus (Vita Marci), ch. 3 — the catalogue of Marcus's philosophical teachers, where Catulus is reckoned among the Stoics. Standard text — Hohl, Teubner.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000, ch. 3 ("Education") — the reconstruction of Marcus's Stoic educational environment; for Catulus, Birley records the same scarcity of sources.
• A. S. L. Farquharson, The Meditations of the Emperor Marcus Antoninus, Oxford 1944, vol. II, ad 1.13 — the standard philological commentary; discusses, among other matters, the unsuccessful attempts to identify Domitius and Athenodotus.
• R. Hard, Marcus Aurelius: Meditations, OWC, Oxford 2011, notes ad 1.13.
• P. Hadot, The Inner Citadel, tr. M. Chase, Harvard 1998 — the general reconstruction of Marcus's Stoic education.
• PIR² — a short prosopographical entry mainly on the basis of the SHA and the Meditations.