Marcus Manilius (fl. 1st century AD) was a Roman poet, astrologer, and author of a poem in five books called Astronomica.
The author of Astronomica is neither quoted nor mentioned by any ancient writer. Even his name is uncertain, but it was probably Marcus Manilius; in the earlier books the author is anonymous, the later give Manilius, Manlius, Mallius. The poem itself implies that the writer lived under Augustus or Tiberius, and that he was a citizen of and resident in Rome. According to the early 1700s classicist, Richard Bentley he was an Asiatic Greek; according to the 19th-century classicist Fridericus Jacob an African. His work is one of great learning; he had studied his subject in the best writers, and generally represents the most advanced views of the ancients on astronomy (or rather astrology).
Manilius frequently imitates Lucretius, whom he resembles in earnestness and originality and in the power of enlivening the dry bones of his subject. Although his diction presents some peculiarities, the style is metrically correct.
The astrological systems of houses, linking human affairs with the circuit of the zodiac, have evolved over the centuries, but they make their first appearance in Astronomicon. The earliest datable surviving horoscope that uses houses in its interpretation is slightly earlier, c. 20 BC. Claudius Ptolemy (c. AD 130 - 170), the father of classical astrology, almost completely ignored houses (Templa as Manlius calls them) in his astrological text, Tetrabiblos.
Julius Firmicus Maternus, who wrote in the time of Constantine, exhibits so many points of resemblance with the work of Manilius that he must either have used him or have followed some work that Manilius also followed. As Firmicus says that hardly any Roman except 'Caesar' (by whom he almost certainly means Germanicus Caesar rather than Julius Caesar), Cicero and Fronto had treated the subject, it is probable that he did not know the work of Manilius. The latest event referred to in the poem is the great defeat of Varus by Arminius in the Battle of the Teutoburg Forest (AD 9). The fifth book was not written until the reign of Tiberius; the work appears to be incomplete, and was probably never published, for it was never quoted by any subsequent writer.
Two manuscripts of Astronomicon made in the 10th and 11th centuries lay hidden in monasteries, one at Gembloux in Brabant (now in Brussels) and another that has come to rest in the library at Leipzig. The unknown text was rediscovered by the humanist Poggio Bracciolini somewhere not very far from Constance, during a break in the sessions of the Council of Constance that he was attending, in 1416 or 1417. The editio princeps of Astronomicon was prepared by the astronomer Regiomontanus, using very corrupted manuscripts, and published in Nuremberg about 1473. The text was critically edited by Joseph Justus Scaliger, whose edition appeared at Paris in 1579 and a second edition, collated with much better manuscripts, at Leiden in 1600. A greatly improved edition was published by Richard Bentley in 1739. The edition of A.E. Housman, published in five volumes from 1903 to 1930, is considered the authoritative edition, although some may find G.P. Goold's edition for the Loeb Classical Library (Harvard, 1977) less intimidating. The first full length monograph in English on Manilius appeared in 2009.