Critodemus was a Greek astrologer who is thought to have lived in the late second or early first century bce. Almost nothing is known about him beyond his dates, and the possibility that he lived on the island of Rhodes. His work survives in only 20 fragments preserved in the extant texts mainly of Vettius Valens (second century ce), but also of Julius Firmicus Maternus (fourth century), Hephaestio (early fifth century) and Rhetorius (sixth or seventh century). An understanding of Critodemus’ work is important because it fills a significant gap in our knowledge of the technical development of astrology between the Babylonian nativity omens of the fifth century bce and the appearance of four complex, extant, first- and second-century ce texts, Manilius’ Astronomica, Valens’ Anthologiae, Dorotheus of Sidon’s Carmen Astrologicum and Claudius Ptolemy’s Tetrabiblos. These texts show astrology in a technically sophisticated form as a mathematically based, highly codified model of the universe, which could be used for almost any purpose, from commenting on the nature of the soul, to diagnosing and treating illness, identifying auspicious times to launch new events, or predicting the future. It had religious, political, social and individual functions. T. sets out to provide a detailed commentary on the surviving fragments of Critodemus’ work, accompanied by the earliest extant Greek text and English translations, providing clues as to the foundations of astrology in the first and second centuries.

To place the book in its wider contemporary academic context, T. begins with a defensive statement:

Such a statement should be unnecessary, given that A. Bouché-Leclercq’s L’Astrologie Grecque was published in 1899 and F. Cumont’s Astrology Among the Greeks and Romans in 1912. And T. cites O.E. Neugebauer’s justification of the study of the history of astrology as necessary for the history of astronomy from The Exact Sciences in Antiquity, published in 1951. Nevertheless, it is noteworthy that T. still felt obliged to justify his work in 2024. At any rate, this book occupies an honourable place in the examination of Greek astrology, which goes back to Bouché-Leclercq.

The volume begins with an introduction that summarises in a few pages the little that is known about second-century bce astrology and speculates that Critodemus might have been a participant in the mysteries of Orpheus. Even though the detail is sparse, T. manages to bring the available material together in a manner that will be useful for historians. The rest of the book is organised in two parts, the first deals with Critodemus’ life, work and reputation, and the second with technical texts. Each section includes the original Greek, an English translation and T.’s commentary. Some of the texts in the first part bring the period to life in a vivid way. Fragment 4 (p. 64) documents Valens’ dismissive assessment of Critodemus (linking him to another astrologer, Petosiris), of whom he wrote ‘let them know that these men showed their science to be groundless by presenting it in an obstruse and involved way’. Valens’ assessment of his work was unsurprisingly, radically different: ‘We on the other hand’, he wrote, ‘provided solutions and not only revived this dying art, but also voted fame for ourselves and initiated other worthy men, seducing them not with the impulse toward money, but by recognising them as lovers of knowledge and enthusiasts’ (p. 64). Critodemus also appears as a source in other works, including Pliny’s Naturalis historia, so we can have no doubt that he was regarded as a significant and respected figure.

The second part of the book includes all the surviving fragments from Greek astrological texts that cite Critodemus on the rules for technical analysis of horoscopes, mainly from Valens. Each chapter treats a different technical topic. Chapter 4 deals with ‘distributions’, which T. speculates are an innovation by Critodemus and are central to all subsequent astrology across western and Indian traditions down to the present day. Chapter 5 considers the terms, subdivisions of zodiac signs, Chapter 6 the time and nature of death, Chapter 7 Klimakteres, critical periods in illness, and Chapter 8 the length of life.

I have very few criticisms of the book. One is that, in places, T. includes notes rather than flowing text. For example, a list of names of natural philosophers, astronomers and astrologers appears on p. 20 with footnotes providing brief biographical information for lesser-known figures. There are places where more introduction to key topics could help. For example, Chapter 4 introduces the technical procedure known as ‘distributions’ or ‘transmissions’. A sentence or two at the beginning of the chapter could have helped readers by summarising this system. Instead, it is left to readers to infer that the reference is to what would now be known as aspect by transit or progression. According to this system planets can be moved around a horoscope according to different measures, the points at which they reach significant relationships to the starting positions of other planets as well as their own starting position, denoting important periods. The index could also be more thorough: although the author index appears to be comprehensive, the general index is missing important topics; for example, klimakteres.

Overall, the book is an essential text for anyone concerned with the development of Greek astrology in the Hellenistic world. This in turn is of significance for astrology’s wider history and transmission. The volume also offers valuable insights into a much overlooked aspect of Greek cosmology, which represented the entire cosmos as a set of mathematical, geometric and linguistic codes that could be applied to the beneficial management of human affairs. It therefore makes a valuable contribution to what we now know as the archaeology of knowledge.