Valerian’s son, Gallienus, turned into a co-emperor a short time after Valerian himself got to the throne.

He had offered a great contribution to the history of military and this was reckoned as the first cavalry-only unit’s commissioning. Thus, it could be sent anywhere in the empire within short period of time. 

He also managed to successfully repel the continuous waves of barbarian invaders, while also managing to finally defeat Postumus that came after a long time and saw two battlefields on thrice occasions.

In addition to these marks of merit, Gallienus was also a tyrant with odd dispositions. He was given a luxurious life when the empire was already suffering from attacks. Hence, this caused the rebellion of multiple armies within the provinces. 

Odenathus, Ingenuus, Quietus, Domitianus of Gaul, Macrianus, Celsus, Trebellianus, Odenathus, Regallianus, Piso, Balista. These are Gallic secessionists, and there may be many more names that may have been lost to history. All unsurping the throne, only to be a victim of crushing defeats at the hands of Gallienus’s forces. 

His luck finally ended while he was trying to besiege another surper, Aureolus. This happened at the hands of despairing soldiers of his own.