MAGNENTIUS (Flavius Magnus Magnentius) ROMAN EMPEROR. — Of barbarian origin, probably Germanic, he had risen to high ranks in the military. He was induced by the foolish conduct of CONSTANS, son of CONSTANTINE, to usurp the imperial purple in agreement with the comes sacrarum largitionum Marcellinus. Constans was killed and M. was recognized as emperor in Gaul, Spain, and Africa (350).
But the wisest and most astute of the three sons of Constantine, Constantius II, could neither recognize the killing of his brother nor tolerate that all the western provinces be separated from the rest of the Empire, especially as other usurpers were arising in Illyricum and at Rome. He therefore prepared for war, which the impulsive M. had in any case rendered inevitable, advancing into Illyricum and the Balkan peninsula. M. was defeated near Mursa (Osijek), but managed to flee and take refuge in Aquileia, from where he later moved into Gaul due to the excessively slow advance of Constantius. Defeated once more at Mons Seleucus (La Batie Neuve), he shut himself up in Lugdunum, where, uncertain of the loyalty of his own men, he killed himself in August 353.