Silvanus (as Zosimus names him ) or Albanus (according to Zonaras ) was a Roman officer of the Third Century AD who came briefly to the notice of history in the reign of Valerian and his co-Emperor Gallienus. He is generally assumed to have been a praetorian prefect under Gallienus.
However, the sources only tell us that he was made the guardian of the Caesar Saloninus by Saloninus's father, the Emperor Gallienus. This seems likely to mean that he exercised a guiding influence over his young protégé as he represented the Imperial Dynasty in the government of the Gallic provinces. In this respect Silvanus/Albanus may be compared with Ingenuus who seems to have exercised a similar function, in loco parentis, in the government of the Illyrian provinces by Saloninus's elder brother, the Caesar Valerian, earlier in the 250s. He would not have been given this office had he not been a seasoned soldier and administrator, but this does not mean that he was Gallienus's Praetorian Prefect.
It was Parker who supposed that Silvanus/Albanus must have held that office(presumably serving at the same time as Successianus who served under Valerian). This suggestion has since been generally accepted without question by academic opinion. However, it assumes that Valerian anticipated Diocletian in appointing (or countenancing the appointment of) such an officer to serve under his co-Emperor (Gallienus) when he (Valerian) went to Syria/Mesopotamia in 258(?) leaving Gallienus in charge in Europe, Egypt and Africa. There is no reason to suppose that such an innovatory measure would have been acceptable to Valerian who was known for his stern reverence for the old Roman constitution. Being Praetorian Prefect was not a necessary condition of being made the guardian of a Licinius Dynnasty Caesar: it has never been seriously suggested that Ingenuus, who seems to have been similarly in loco parentis in respect of Saloninus's brother, the Caesar Valerian in the Illyrian provinces, was so honoured.
It is not impossible to suppose that Gallienus was expected to manage without a Praetorian Prefect until after Valerian (and Successianus) were captured by Shapur I in 260. Then Gallienus became sole Emperor, no longer subject to his father's potestas patriae and was free to appoint Volusianus (L. Petronius Taurus), his own man, to that position.
Praetorian Prefect or not, in 260 Silvanus/Albanus fell into dispute with Postumus over the disposition of loot which the latter had seized from a party of German raiders in Gaul. Postumus's army, infuriated, then proclaimed their man Emperor and attacked Silvanus/Albanus and the young Caesar in Cologne. The pair were eventually given up by the citizens and killed by Postumus's men.