Clinton, (F. H. vol. iii. pp. 535, 538,) who puts Hero as low down as the end of the second century B. C., proceeds on the following evidence: Athenæus (vol. iv. p. 174, edit. Schweighæuser) quotes one Aristocles as saying, in a work περὶ χορῶν, of the water-organ, φασὶ τοῦτο εὑρῆσθαι ὑπὸ Κτησιβίου κουρέως ἐνταῦθα οἰκοῦντος ἐν τῇ Ἀσπενδίᾳ ἐπὶ τοῦ δευτέρου Εὐεργέτου· διαπρέψαι τέ φασι μεγάλως. Now Euergetes II. (Ptolemy VII.) reigned from B. C. 170 to B. C. 117, and hence Clinton assigns Hero, the pupil of Ctesibius, to the reign of Ptolemy VIII. that is, to B. C. 117–81. Fabricius, on the other hand, (Bibi. Græc. vol. iv. pp. 222, 234, edit. Harl.) setting out from an entirely different datum, places him more than a hundred years earlier, in the time of Ptolemy Philadelphus (Euergetes I.): Athenæus Mechanicus, (one of the mechanical writers whose works are printed in the _Veterum Mathematicorum Opera_), in his treatise περὶ μηχανημάτων, p. 8, speaks of Ctesibius as a contemporary; his words are Κτησίβιος ὁ Ἀσκληνὸς, ὁ ἐν Ἀλεξανδρείᾳ μηχανικός. This treatise is dedicated to a Marcellus, and Fabricius, assuming, after Hero junior, this Marcellus to be the conqueror of Syracuse, has hence assigned Ctesibius and Hero to the reigns of the second and third Ptolemies (B. C. 285–222). Of these conflicting dates that assigned by Clinton has been generally adopted. The question is discussed at some length by Schweighæuser, in a note on the passage of Athenæus referred to above: he deems the identification of the patron of Athenæus Mechanicus with the conqueror of Syracuse to be unwarranted, and, besides, thinks it most unlikely that at so early a period a Greek should dedicate a work on military engines to any Roman. But from the expression employed by Athenæus, (ὦ σεμνότατε Μάρκελλε,) it may be inferred that his patron was a man of very exalted rank; and the second objection from the alleged improbability that a Greek should dedicate such a work to a Roman at that period will hardly be thought to apply at the period referred to, while the skill displayed by Marcellus in the siege of Syracuse, and the regret expressed by him for the fate of Archimedes, (whether genuine or not,) may well have suggested the dedication to him of a work on military engineering. The assumption of Fabricius, then, is, in itself, not to be too hastily rejected; and it will be seen that it is not so irreconcileable with the statement of Aristocles as has been supposed. Fabricius has carried back the date further than his argument requires or even warrants. Marcellus was killed B. C. 208: Athenæus might have inscribed his work to him about B. C. 212 or 210; at this period, then, we must suppose Ctesibius to have been known as a philosopher,[2] but he may have lived far into the succeeding century,—possibly even into the reign of Euergetes II. (B. C. 170–117); Hero would thus be placed about B. C. 150, a result by