MARCUS or CAIUS, a Latin poet, the author of Astronomica, an astrological treatise in five books. Regarding the facts of his life, and even his true name, great uncertainty prevails. In different MSS. he is called Manilius and Mallius, and other names slightly varying from each other. Different critics severally suppose him to be the senator Manilius; Manilius called the founder of astrology; and Manilius the mathematician; to all of whom allusion is made by Pliny in his Natural History. Yet all these suppositions rest on no surer grounds than the identity of the names, and the fact that all the persons mentioned must have been in a greater or less degree acquainted with astrology. From the internal evidence of his poem, it has been argued that Manilius flourished in the age of Tiberius, although Bentley places him in the Augustan age. The same great critic supposes him to have been a native of Asia, a conjecture that is by no means refuted by the circumstance, that Manilius talks in his poem as if he were a Roman citizen, and were living at the period at which he writes in the Roman capital.

The want of finish, and the abrupt conclusion of the Astronomica, evidently indicate that it was left incomplete. As a philosopher, Manilius has shown great talent in using all the astronomical lore of his day in selecting the most sagacious of conflicting opinions, and in starting some conjectures which have been fully verified in modern times. Yet, as a poet, his imperfect taste, and his pointless and inharmonious diction, fall far short of that genius which alone can elevate a scientific subject into the sphere of true poetry. The Astronomica was first discovered in manuscript by Poggio in 1416. From this copy the editio princeps was printed by Regiomontanus, 4to, Nuremberg; probably about 1472 or 1473. The standard edition is that of Bentley, 4to, London, 1739. A translation into English verse, by Thomas Creech, was published, Svo, London, 1697, 1700.