Chosen by Galerius as Caesar upon Diocletian's abdication, Severus would spend several years in the VP post until Constantius died. In what may have then been a shocking turn of events, rather than Severus automatically becoming the new emperor, the title passed instead to Constantius's son Constantine. On hearing of this Galerius threatened a major civil war. Constantine reached an agreement that ended in Severus claiming the title while he took a demotion to Caesar.
Still, it was becoming evident that Constantine was poised to becoming emperor some day and this most aggravated Maxentius whose father Maximianus sidestepped him for the good of the system. With a "no fair" attitude, Maxentius appropriated the city's garrisons and had himself made emperor back in Rome. This, naturally, created a problem for Severus which he had to deal with. He marched his soldiers down into Italy but the expedition met with failure. Maxentius was too powerful and influential and the forces of Severus were demoralized and many deserted him. The loss of manpower put him into retreat mode at the same time that Maxentius was ramping up an offensive. Severus soon found himself the unfortunate guest of the rebel who had him executed.
RIC 27b (Cyzicus) Follis Obv: IMPCFLVALSEVERVSPFAVG. Head right, laureate.
Rev: GENIOPOPVLIROMANI Exe: */K(officina) - Genuis standing left, modius on head, naked but for chlamys over left shoulder, right hand holding patera, left holding cornucopiae.