He shared control of the western half of the empire with Constantine I, but spent most of his short reign in a civil war against the usurper Maxentius, who later killed him and took over Italy.

[4] Diocletian acquiesced and Severus succeeded to the post of caesar on 1 May 305, thus becoming the junior colleague of Constantius I, augustus of the western half of empire.

[5] When Maxentius, the son of the retired emperor Maximian, revolted at Rome in October, Galerius sent Severus to suppress the rebellion.

Severus moved towards Rome from his capital, Mediolanum, at the head of an army previously commanded by Maximian.

[6] Despite Maximian's assurance, Severus was nonetheless displayed as a captive and later imprisoned at Tres Tabernae, near the current Cisterna di Latina.