Posthumus Revolt - A History of the Roman Empire

Odinathus kept the sasonis at bay and reasserted roman dominion over territory that sharper had annexed. Postumus ruled in direct competition to gallienus, where the eastern provinces still recognized the overall legitimacy of the roman emperor. The west had gone over to posthumus completely. This was an affront that gallienus could not tolerate. Gallienus was able to establish a permanent beach head on the far side of the alps, but he was unable to decisively defeat postumus and reunite the empire.