[1] He may have secured his first appointments before the Licinian Dynasty – (Valerian and his son Gallienus) – acceded to the Empire in 253 AD, but it was in the course of their reign that his upward progress achieved an almost unprecedented momentum and the second factor seems to have been a consequence of the first.
The nature of his relationship to the Licinii is uncertain, but it seems likely that a common origin in the Etruscan region of central Italy at least predisposed Gallienus in his favour and he seems to have been that emperor's most trusted servant and adviser during the period of his sole reign - 260(?
In chronological order they are: It is generally assumed that, despite being raised to the consulate, Volusianus nevertheless continued to serve as Praetorian Prefect until his appointment as Praefectus Urbi in 267 - see below.
During the High Empire (i.e., prior to the reign of Diocletian) the extent to which individual princes maintained the social subordination of the men they entrusted with the Equestrian Prefectures[f] to the senatorial holders of the Great Magistracies inherited from the Republic and especially to the consulate, was regarded as a measure of their fidelity to the legacy of the first Emperor.
[24][g] Volusianus was the first Praetorian prefect to hold that office in tandem with the consulate since 203 AD when C. Fulvius Plautianus had exercised it under Septimius Severus - not a happy precedent from the point of view of those who held dear the principles of the Augustan Constitutional settlement.
[26][h] It is authoritatively suggested that, in the second half of the third century, Praetorian Prefects did exercise some sort of supremacy in military matters vice principis (i.e., 'on behalf of the emperor').
It is also possible that by raising Volusianus to the Senate while keeping him on as Praetorian prefect, Gallienus was seeking to increase his social standing and thus his ability to act as his effective viceroy in Italy outside Rome - one of the major functions of the praetorian prefecture - and to deal on equal terms with the senatorial officials who were being increasingly appointed as Correctores of the Italian regiones (in effect, making them equivalent to provincial governors of these districts) and Curatores (supervisors of the City-Councils).
[28] However, if Gallienus's chief motive in 261 AD was, indeed, to ensure his control of the Senate in a moment of crisis by putting his trusted favorite at its head, this does not seem to have been a continuing concern.
(So far as is known, Heraclianus's experience was wholly in the military field and he had no exposure to civilian administration, which constituted a major part of the remit of the Praetorian Prefecture).
[30] Whatever the merit of this suggestion, the savagery shown by the Senate against Gallienus's family and supporters (probably including Volusianus) after his murder in 268 is strongly indicative of a legacy of unresolved issues between a powerful faction of the order and the emperor that could well have built up over a number of years.
[16] There is no record of him taking part in that campaign nor is he mentioned by any ancient source in connection with the conspiracy that led to Gallienus's assassination by his leading military officers.