Thus Lactantius refers to the "vicarii praefectorum" as being active already in Diocletian's time. Other sources from Diocletian's reign mention one Aurelius Agricolanus who was an "agens vices praefectorum praetorio" active in Hispania and condemned a centurion named Marcellus to be executed for his Christianity, as well as an Aemilianus Rusticianus, who is considered by some scholars to have been the first vicar of the Diocese of the East that we know of. Lactantius also mentions one Sossianus Hierocles as an "ex vicario" active in the East in this period. Septimius Valentio is also attested as "agens vices praefectorum praetorio" of Rome between 293 and 296. However, these sources do not prove that these "vicarii" or "agentes vices" were already in charge of dioceses with a well-defined and stable territory. Septimius Valentio in particular was definitely the commander of the Praetorian Guard during a period when the Praetorian Prefect was absent from the city, but was not in charge of Italia Suburbicaria. According to Zuckerman, the establishment of the dioceses should instead be dated to around AD 313/14, after the annexation of Armenia into the Roman empire and the meeting of Constantine and Licinius in Mediolanum. The matter remains controversial.