As intimated above, Aper is identified with the Aper who was commemorated on the epigraph dated 267-8 found at Poetovio, in Pannonia Superior (now Ptuj, Slovenia). The inscription describes Aper as a vir egregius praepositus legionum V Macedonicae atque XIII Geminae. Poetovio was an important fortress on the River Sava which controlled the approaches to Italy through the Julian Alps It cannot be determined whether Aper commanded the fortress garrison or whether he answered to a superior officer who would probably have been styed as a dux The force under Aper's command would have consisted of elements (i.e. vexillationes) of the legions mentioned rather than the legions themselves, (There is no known instance of a praepositus commanding a full legionary establishment, let alone two).