17. MECHANICUS, a Greek mathematical writer, whose period is not exactly known. He was later, probably much later, than Claudius Ptolemaeus. He wrote his only known work for the gratification of his friend Theodorus, whose fellow-workman in some mechanical pursuit he had been. It is doubted whether this Theodorus was the person of that name to whom Proclus inscribed his treatise De Providentia et Fato; or a later Theodorus, an engineer, who defendedd Dara in the war between the emperor Justinian I. and the Persian king, Chosroes I. (Procop. de Bell. Persico, 2.13): more probably it was the latter. Leontius also states that he had constructed a sphere or celestial globe, after the description of Aratus, for an Elpidius, who was perhaps the Elpidius sent by the emperor Maurice (A. D. 583) on an embassy to the Chagan ofthe Avars. (Theophan. Chronog. p.214, ed. Paris, p. 170, ed. Venice, vol. i. p. 390, ed. Bonn.) It may then be considered that Leontius lived in the reign of Justinian and his successors, in the latter part of the sixth century.