From Classic Encyclopedia 1911
POSIDONIUS (c. 130-50 B.C.), nicknamed "the Athlete," Stoic philosopher, the most learned man of his time (so Strabo τῶν καθ’ ἡμᾶς φιλοσόφων πολυμαθέστατος, Galen ἐπιστημονικώτατος) and perhaps of all the school. A native of Apamea in Syria and a pupil of Panaetius, he spent after his teacher's death many years in travel and scientific researches in Spain (particularly at Gades), Africa, Italy, Gaul, Liguria, Sicily and on the eastern shores of the Adriatic. When he settled as a teacher at Rhodes (hence his surname "the Rhodian") his fame attracted numerous scholars; next to Panaetius he did most, by writings and personal intercourse, to spread Stoicism in the Roman world, and he became well known to many leading men, such as Marius, Rutilius Rufus, Pompey and Cicero. The last-named studied under him (78-77 B.C.), and speaks as his admirer and friend. He visited Rome, e.g. on an embassy in 86 B.C., but probably did not settle there as a teacher.
His works, now lost, were written in an attractive style and proved a mine of information to later writers. The titles and subjects of more than twenty of them are known. In common with other Stoics of the middle period, he displayed eclectic tendencies, following the older Stoics, Panaetius, Plato and Aristotle. His admiration for Plato led him to write a commentary on the Timaeus; in another way it is shown by important modifications which he made in psychological doctrine. Unquestionably more of a polymath than a philosopher, he appears uncritical and superficial. But at the time his spirit of inquiry provoked Strabo's criticism as something alien to the school (τὸ αἰτιολογικὸν καὶ τὸ ἀριστοτέλιζον, ὅπερ ἐκκλίνουσιν οἱ ἡμέτεροι). In natural science, geography, natural history, mathematics and astronomy he took a genuine interest. He sought to determine the distance and magnitude of the sun, to calculate the diameter of the earth and the influence of the moon on the tides. His history of the period from 146 to 88 B.C., in fifty-two books, must have been a valuable storehouse of facts. Cicero, who submitted to his criticism the memoirs which he had written in Greek of his consulship, made use of writings of Posidonius in De natura deorum, bk. ii., and De divinatione, bk. i., and the author of the pseudo-Aristotelian treatise De mundo also borrowed from him.
See Zeller, Philosophie der Griechen, iii. 1, 570-584 (in Eng. trans., Eclecticism, 56-70); C. Müller, Fragmenta historicorum graecorum, iii. 245-296; J. Bake, Posidonii Rhodii reliquiae (Leiden, 1810), a valuable monograph; R. Scheppig, De Posidonio rerum gentium terrarum scriptore (Berlin, 1869); R. Hirzel, Untersuchungen zu Ciceros philosophischen Schriften, i. 191 seq., ii. 257 seq., 325 seq., 477-535, 756-789, iii. 342-378 (Leipzig, 1877); Thiaucourt, Essai sur les traités philosophiques de Cicéron (Paris, 1885); Schmekel, Die Philosophie der mittlern Stoa (1892); Arnold, Untersuchungen über Theophanes von Mytilene and Posidonius von Apamea (1882). (See also STOICS.)