Podcast episode

Episode 66: Astrology, Politics, and Platonism in the Early Empire: The Case of Thrasyllus

In this episode we return, as promised, to the fascinating and little-known figure of Tiberius Claudius Thrasyllus, Greek astrologer, philosopher, philologist, and bosom-companion of the emperor Tiberius. We explore the evidence for the man’s life, as well as some of the great stories about him in our sources which are probably not to be read as historically accurate.

We also go off on a few relevant tangents, discussing:

  • the importance of astrology in the politics of the early empire,
  • the widespread belief in deterministic fate in this period and its eventual downfall in late antiquity,
  • the curious fact that astrology would go on to flourish under Christianity, despite the many condemnations of it in authoritative church writers, and
  • the question of whether it makes sense to discuss astrology in the Roman context as ‘esotericism’ at all.

Finally, we discuss Thrasyllus’ most lasting contribution to the history of ideas and esotericism: his editing of the Platonic corpus, his possible tampering with Plato’s texts, and his possible forging of a crucial bit of Platonic esotericism, the notorious Second Platonic Epistle.

Works Discussed in this Episode:

(Note: for Suetonius, the English translation is by J. C. Rolfe. Cassius Dio translated by Earnest Cary. Tacitus is Church and Brodribb’s translation. References below to ‘Cat.’ are to the Catalogus Codicum Astrologorum Graecorum, for which see the Recommended Reading)


  • Aratus: Aratus of Soli (4th-3rd cen. BCE) wrote many works on astronomy. His Phænomena is a didactic poem setting to metre the scientific work of Eudoxus of Cnidos, whom we saw working at Plato’s Academy in the ‘astronomy department’ in Episode 40. The Latin version of Aratus’ Phaenomena from the pen of Tiberius’ nephew (and adopted son), Germanicus survives, edited by Breysig, Berlin 1967.
  • Cassius Dio: Tiberius becomes a lifelong practicing astrologer: 55, 11, 1.
  • The Gladiator’s Tombstone: Corpus Inscriptionum Latinarum 5: 354. no. 3466: Planetam suum properare vos moneo; in Nemesi ne fidem habeatis; sic sum deceptus. Cf. CIL 6 : 2743, no. 28044, CIL 6, 4 : 2675, no. 27140.
  • Juvenal cites Thrasyllus’ astral lore and possible arithmological treatise: 6, 569-76.
  • Manilius on his intended audience: Astronomica 2, v. 136 ff.
  • ‘Plato’: The ‘King of All’ passage in the Second Letter: 312d7-313a6.
  • Porphyry: Plot. 21
  • Suetonius: On Tiberius’ cliff-of-doom on Rhodes, and Thrasyllus’ prediction that the ship coming in bore good news for the future emperor: Tib. 14, 4.
  • Tacitus: Aside on astrology and fate: Annales VI, 22 1. Tiberius’ cliff-of-doom on Rhodes: An. VI 21, 1. Tiberius becomes a lifelong practicing astrologer: An. VI, 21.
  • Themistius: Or. 5; 8; 11; 34.
  • Thrasyllus: Thrasyllus’ full Roman name is attested in a Smyrna inscription, CIL 3.7107 = IGR 4.1392. The identity of the Platonist philosopher Thrasyllus and the imperial astrologer (who might otherwise have been thought different guys with the same name) is attested by a scholiast (marginal commentator) to Juvenal 6.576, T1a Tarrant; cf. T3-4. Hung out with Augustus: Suet. Aug. 98, 4. Taught Tiberius astrology: Josephus Antiquities 18.211-218. Vettius Valens cites the astrological writings of Thrasyllus: Anth. 9, 11. Hephæstion of Thebes ditto: Cat. 6: 100, 11; cf. 8, 2. Teachings on the thema mundi, the heptazonos, the doctrine of the twelve places and the ‘physis’ of zodiacal signs and planets: see Cat. 8, 3: 99-101. On the tetralogies: D.L. 3 56-61. Although none of Thrasyllus’ astrological writings survive in extenso, an epitome of one, existing in a single MS, can be read at Cat. 8, 3 : 99-101 (see Recommended Reading below).


  • Cramer, F., 1954. Astrology in Roman Law and Politics. American Philosophical Society, Philadelphia, PA.
  • Tarrant, H., 1993. Thrasyllan Platonism. Cornell University Press, Ithaca, NY and London. Tarrant argues that the prominent astrologer Balbillus may not have been the son of Thrasyllus p. 10.

Recommended Reading:

  • Pierre Boudreaux, editor. Catalogus Codicum Astrologorum Graecorum, volume 8, Part 3. Lamertin, Brussels, 1912. See pp. 99-101 for the text of the sole surviving astrological writing of Thrasyllus, the so-called Pinax (‘Table of Contents’), which at least lets us know the kind of things he was writing about.
  • F.H. Cramer. Astrology in Roman Law and Politics. American Philosophical Society, Philadelphia, PA, 1954.
  • M.R. Dunn. The Organization of the Platonic Corpus between the First Century B.C. and the Second Century A.D. PhD thesis, Yale, Ann Arbor, MI, 1975.
  • Steven J. Green. Disclosure and Discretion in Roman Astrology: Manilius and his Augustan Contemporaries. Oxford University Press, Oxford, 2014.
  • Alexander Haggerty Krappe. ‘Tiberius and Thrasyllus’. The American Journal of Philology, 48(4): 359-66, 1927.
  • John Rist. ‘Neopythagoreanism and Plato’s Second Letter’. Phronesis , 10(1): 78-81, 1965.
  • Schmidt, R.H., trans. and comm. Antiochus, with Porphyry, Rhetorius, Serapio, Thrasyllus, Antigonus et al., Definitions and Foundations. The Golden Hind Press, Cumberland, MD, 2009. See pp. 341-345 for Thrasyllus.
  • H. Tarrant. ‘Middle Platonism and the Seventh Epistle’. Phronesis , 28(1):75-103,
  • Idem. Thrasyllan Platonism. Cornell University Press, Ithaca and London, 1993.


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