It is under Augustus that astrology comes to the fore in literature. There is the first astrological work in Latin, indeed the first classical astrological work to survive in its original form, the didactic poem of Manilius. He followed a Greek tradition in writing in verse: not only was Aratus' Phaenomena a model, but, as we have seen, Nechepso was said to have written thirteen books in verse on horoscopic astrology. Lucretius had also offered a Latin example, in writing his great exposition of Epicurean philosophy in verse. But Virgil's didactic poem on agriculture, the Georgics, written for the literary circle centred on the new imperial court, was probably a more significant predecessor. It may well be the case that Manilius was no more an astrologer than Virgil was a farmer, and that much of the appeal was in the difficulty of versifying such unlikely material. At any rate, it offers the sort of synthesis of astrological doctrine the author thought suitable for the Roman elite, and dresses it up with a rhetoric of fatalism which clearly recalls Stoic ideas. Since it is the first theoretical work to survive almost in its entirety, it is worth looking at its contents in some detail. (The technical terms are explained in Chapter 4.)
The first book, after a brief account of cosmological speculations, concluding with the view that the Earth is composed of four elements, offers an elementary description of the heavens and ends with a discussion of comets as omens. It seems to visualise the Babylonians as the originators of astronomy and the Egyptians as the inventors of astrology. In the mention of the 'kings' and 'priests' who were responsible, there is presumably a poetic allusion to Nechepso and Petosiris. Book 2 gives the characteristics of the signs of the zodiac, expounds their geometrical relationships, the zodiacal and planetary dodecatemories, the cardinal points, the Twelve Places and the Eight Places. Book 3 describes the twelve Lots, the rising times and the Time-Lords, explains how to calculate the length of life, and concludes with a discussion of tropic signs. The fourth book gives an account of the characteristics of the zodiac signs imparted to the native, describes the decans and the influences of some of the individual degrees of the zodiac, depicts a map of the world along with the zodiacal rulers of each part, and finishes with a discussion of the effects of eclipses on different signs. The final book recounts the paranatellonta, or stars rising and setting with the signs. It seems likely that a treatment of planetary influences has dropped out at this point, and the following account of stellar magnitudes, with which the poet closes, may also be incomplete.
Apart from Manilius, Augustan literature furnishes us with ample evidence that astrology had become very fashionable in circles close to the court. For the most part, there are only occasional allusions to astrology, but in one case an astrologer is imagined as addressing the poem to the poet. In most cases the tone seems clearly lighthearted. However, the sudden appearance of astrological references can hardly be an accident—as in other areas, the poets pick up themes of imperial self-presentation.
Augustus was taking a risk in using astrology to legitimate his position, because he was opening up a way for others to follow. The risks were obviously apparent to him, because, in 11 CE, when he did not look likely to live much longer, he had a measure passed forbidding astrological consultations to be made in private, or to concern anyone's death. We do not hear of this measure being used until his successor Tiberius was in place. Tiberius is presented in our sources as a tyrannical ruler, and it is where tyrants appear that astrology is a leitmotiv in the literature. He is the first emperor to be reported to have a court astrologer. The story goes that he met Thrasyllus while in exile in Rhodes, when he was out of favour with Augustus. His practice was to test astrologers when he needed their guidance. If they seemed unreliable, or fraudulent, they would be thrown off the cliff on the way back from his house, which was at the top of a precipice. When Tiberius questioned Thrasyllus, he was impressed by his answers, which included a prediction that he, Tiberius, would succeed Augustus. The future emperor then put his test-question: how did Thrasyllus' own horoscope appear for that year and day:
Thrasyllus, after measuring the positions and distances of the stars, hesitated, then showed alarm. The more he looked, the greater his astonishment and fright. Then he cried that a critical and perhaps fatal emergency was upon him. Tiberius clasped him, commending his divination of peril, and promising that he would escape it. Thrasyllus was admitted among his closest friends, his pronouncements were regarded as oracular.28
This tale had sufficient mythical quality for it to be told and retold in versions of the life of Alexander the Great. Its appeal doubtless lay in its confrontation of the seer with the equivalent of the dictum Physician, heal thyself. For once, in the story, the seer comes up trumps.
Nevertheless, regardless of the folk-tale element in the story, Thrasyllus was real enough. An anecdote in Suetonius' 'Life of Augustus' presents him as a literary man rather than as an astrologer.29 He is cited by later astrologers, and we have an epitome of one of his treatises, the Pinax, in which he cited Petosiris, Nechepso and Hermes. This is in fact the earliest securely dated mention of Hermes: Thrasyllus was thus one channel through which Hermetic astrology reached Rome. His friendship with Tiberius certainly brought rewards: though he had only received citizenship under Augustus, his daughter married the knight L.Ennius in about 15 CE. When Ennius was charged with lèse-majesté in 22, Tiberius vetoed the charge. Thrasyllus' granddaughter by that marriage married Naevius Sutorius Macro, the knight who was to act virtually as Tiberius' regent in his last years.
The first case in which the crime of astrological enquiry was linked with treason came in 16 CE. Marcus Scribonius Libo Drusus, who was a young man related to the imperial family, had apparently consulted astrologers, magicians and dream-interpreters. The accusers argued that 'mysterious or sinister marks' made against the names of members of the imperial family and senators were in his handwriting, and a necromancer testified that he had been asked to use magic on Libo's behalf. Apart from Tacitus, who was hostile to Tiberius, the sources tend to agree that Libo was planning a coup. He committed suicide before the case could come to trial. The Senate immediately passed two decrees against astrologers and other diviners, and two men, either astrologers or magicians, were executed publicly, one being thrown off the Tarpeian Rock and the other beaten to death with rods to the sound of bugles.30
Naturally, Thrasyllus was not expelled; sources still reveal him advising the emperor. Indeed, Tiberius is envisaged by Juvenal in his years of self-imposed retreat on the island of Capri, as surrounded by a flock of astrologers.31 According to Dio, their job was to find out the men whose nativities revealed an imperial future, so that they could be exterminated.32 Various items of astrological advice to Tiberius are recorded: supposedly, he was told that Galba would become emperor, but only at an advanced age, that Gaius (Caligula) had as much chance of becoming emperor as of riding across the Bay of Baiae on horseback. Thrasyllus was also said to have prevented him from ordering the deaths of many, assuring him that he had many years of life left.33
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