Saloninus was born around the year 242. His father was the later emperor Gallienus, his mother Cornelia Salonina, a Greek from Bithynia. In 258 Saloninus was appointed Caesar by his father (just like his older brother Valerian II, who had died around 258) and sent to Gaul to make sure his father's authority was respected there. (The title Caesar in Imperial nomenclature indicated that the holder was the Crown Prince and first in line of succession after the Augustus, the title reserved for the ruling Emperor). Like Valerian II, who was made the ward of Ingenuus, governor of the Illyrian provinces, Saloninus was put under the protection of the praetorian prefect Silvanus (otherwise named as Albanus) As Caesar in Gaul Saloninus had his main seat in Cologne.

Bray conjectures that Saloninus's appointment as Caesar, like that of his elder brother, Valerian II, in Illyria, was made at the instigation of Valerian I who was, simultaneously, the senior Emperor (Augustus) and grandfather of the two young Caesars and, as head of the Licinius clan, exercised also the patria potestas[1] over all members of the Imperial family, including his son Gallienus, his co-Emperor (and co-Augustus). Bray suggests that Valerian's motive in making these appointments was securing the succession and establishing a lasting imperial dynasty. We do not know how Valerian envisaged his grandson interacting with the existing governors and military commanders of the Gallic provinces. There is no reason to suppose that he ever thought the thing through as systematically as Diocletian when he established the Tetrarchy some thirty years later. However, Silvanus must have been a seasoned soldier and administrator, and he does seem to have harboured the notion that, as guardian of Saloninus, he should exercise real authority in Gaul. This was demonstrated by the circumstances in which he fell out with the usurper Postumus.

...
Wikipedia