 Following Galerius ' recognition of Constantine as caesar , Constantine 's portrait was brought to Rome , as was customary . Maxentius mocked the portrait 's subject as the son of a harlot , and lamented his own powerlessness . Maxentius , envious of Constantine 's authority , seized the title of emperor on 28 October 306 AD . Galerius refused to recognize him , but failed to unseat him . Galerius sent Severus against Maxentius , but during the campaign , Severus ' armies , previously under command of Maxentius ' father Maximian , defected , and Severus was seized and imprisoned . Maximian , brought out of retirement by his son 's rebellion , left for Gaul to confer with Constantine in late 307 AD . He offered to marry his daughter Fausta to Constantine , and elevate him to Augustan rank . In return , Constantine would reaffirm the old family alliance between Maximian and Constantius , and offer support to Maxentius ' cause in Italy . Constantine accepted , and married Fausta in Trier in late summer 307 AD . Constantine now gave Maxentius his meagre support , offering Maxentius political recognition . 
