Gallienus

253 - 268

Gallienus, Valerian's son, became co-emperor shortly after Valerian himself ascended the throne. His greatest contribution to military history was the first commissioning of a cavalry-only unit which could be dispatched anywhere within the empire within short order. He was also successful in repelling wave after wave of barbarian invaders as well as finally defeating Postumus after a prolonged period which saw the two in battlefields on three different occasions.

Asides from these marks of merit, Gallienus was a cruel tyrant of an oddly mild disposition. Given to a life of luxury at a time when the empire was suffering endless bouts of attacks this procured the rebellion of many armies in the provinces. Ingenuus, Macrianus, Quietus, Balista, Domitianus of Gaul, Regallianus, Zenobia, Celsus, Odenathus, Trebellianus, Piso, the Gallic secessionists and possibly many more whose names are lost to history all usurped the throne only to have met crushing defeats by the forces of Gallienus. His luck finally ran out while besieging another usurper, Aureolus, at the hands of his own despairing soldiers.