Athenaeus (2) Mechanicus is the named author of a surviving treatise On Machines; military ones, for use in siege-warfare. The work is addressed to a ‘Marcellus,’ and nowadays orthodoxy identifies him with M. Claudius Marcellus, the short-lived (42–23 bce) nephew & son-in-law of Augustus. That in turn makes it plausible that the writer himself is Athenaeus of Seleucia-on-the-Calycadnus, a Cilician Greek intellectual known to have been in Rome in the 20s, and a contemporary, in that milieu, of Vitruvius. There is indeed material common to A.’s treatise and to sections of Book 10 of Vitruvius' On Architecture—material that, it seems, they took from their teacher Agesistratus of (?)Rhodes.Short and not always coherent though it is, the On Machines has a two-fold importance. One is in the material mentioned already: Athenaeus and Vitruvius in tandem (together with a middle-Byzantine version of the same material) provide a succinct but useful summary history of military machinery from its beginnings to the early Hellenistic period, highlighting especially the mechanici who served Alexander the Great.