Roman Emperor. Flavius Magnus Magnentius was born about 303 CE at Ambiana (Amiens). His father was a Breton (sometimes identified as British) and may have come to Amiens as an artisan in the entourage of Constantius Chlorus or Constantine. His mother was Frankish and a soothsayer who made several predictions concerning Magnentius, all of which proved to be true. Magnentius joined the army of Constantine I and may have caught the attention of the emperor. He flourished in the army and rose through the ranks to become a staff officer, then comes rei militaris in charge of two prestigious legions - the Ioviani and Herculianai. Constans was deeply unpopular due to blatant corruption in his court and his tyrannical attitude. On January 18, 350 CE Magnentius appearing in the imperial purple robes at a birthday party held by Marcellinus, the finance minister of Constans, at Augustodunum (Autun). He was proclaimed Augustus and Constans fled toward Spain, but was caught by Gaiso, one of Magnentius' agents, and killed. Magnentius hoped to come to terms with Constantius II, the last remaining son of Constantine, but his diplomatic efforts were for nothing. A challenge to Magnentius came from Nepotian, a nephew of Constantine I, in June 350, but the threat was quickly eliminated when a force led by the praetorian prefect Anicetus took Rome and killed Nepotian. The whole of the western empire, Spain, Britain, Gaul, Italy and Africa, now lay in Magnentius' hands. However, a more serious challenge to Magnentius' power soon arose. The legions of Illyria, critical for Magnentius to extend his control eastward, proclaimed the magister peditum, Vetranio, emperor on March 1, 350. Vetranio was an unlikely choice, and is described as being illiterate and dull-witted. Vetranio was acclaimed emperor possibly at the instigation of Constantia in order to hold the middle Danube for her brother or the soldiers objected to the usurpation of a barbarian as their emperor. In any case, Magnentius was thwarted in his attempts to expand his influence. Constantius and Vetranio soon came to terms where the Illyrian legions agree to accept Constantius as their emperor and Vetranio retired to private life. Magnentius opened negotiations with Constantius to have himself recognized as the rightful ruler of the West. As part of his appeal, he issued coins in Constantius' name and proposed that the emperor marry his daughter; Magnentius, to complete the alliance, would marry Constantia. The rebellion of Nepotian forced Magnentius to realize that war was inevitable. Even while negotiations were continuing, Magnentius raised large sums of money and built an army largely made up of his fellow Franks, Saxons and Germans. His army eventually outnumbered the forces Constantius had at his disposal. Magnentius' brother, Flavius Magnus Decentius, was raised to the rank of Caesar around June. Decentius was given the task of protecting the provinces beyond the Alps but, initially, his role probably would have been to assist his brother should rebellion break out. The usual time given for Decentius' elevation is March 351, at the same time Gallus was made Caesar by Constantius. This date seems to square with Decentius' consulship (held in 352). However, even if Decentius was named Caesar in 350 he would have waited for his consulship since Magnentius and Gaiso had already been named to fill the offices for 351. Around the same time, Magnentius married Justina, who is thought to have been a daughter of Justus, a praetorian prefect of Licinius and consul in 328, who married a daughter of Crispus Caesar. This gave Magnentius a family connection to Constantius since his wife was a great-granddaughter of Constantine. Constans, following the laws initiated by his father in the East, had prohibited pagan sacrifices and probably seized temple treasure late in his reign. Magnentius overturned the prohibition. The favor that Magnentius showed to pagans has been construed to mean the emperor was pagan himself. The army was recruited from young men living in the rural countryside where Christianity had made no inroads. Constantine was concerned with maintaining the loyalty of his army and so made no attempt to convert the soldiers to Christianity. It is impossible to be certain what faith Magnentius practiced. However, he had to exercise the same constraint as Constantine with regard to his army so as not to offend Christians or pagans. The overturning of Constans' prohibition of pagan sacrifices may have stemmed from a need to appeal for pagan support. If Magnentius acted from his own beliefs, we have no way of being certain. During the winter of 351, Magnentius closed the passes through the Julian Alps into Italy. He had made a triumphal entry into Aquileia, possibly in January, and would use the city as his base of operations. In the spring, Constantius tried to break through into Italy but was repulsed at Altrans. Magnentius sought to pursue his advantage and marched into Pannonia Superior, occupying Siscia by the summer. He did not linger at Siscia and continued his march to Sirmium. There, he failed to capture the city when met with token resistance. Resuming his march, Magnentius laid siege to the city of Mursa where his forces were kept at bay by stiff resistance from the citizens. Constantius, who had earlier pulled his forces back to Cibalis, marched to relieve the city. On September 28, 351, the armies met on a plain outside of Mursa. Constantius positioned his forces with the Drava River to his right and the Danube to his back; his soldiers were given little choice but to win or be annihilated. His Persian styled cavalry was grouped in both wings with archers; heavy infantry occupied the center with additional archers and slingers in the rear. Battle was joined in late afternoon and fighting was fierce on both sides. Julian says Constantius' left outflanked Magnentius and his phalanx was overwhelmed. Eventually, it was Constantius' mail-clad cavalry that made the difference; they overwhelmed Magnentius' right and threw the entire line into confusion. The soldiers on both sides were so enraged that they continued to fight even after night had fallen. Magnentius was forced to withdraw but Constantius was not able to take advantage of his opponent's weakness. This was a Pyrrhic victory. As many as 54,000 dead (Magnentius' dead were put at 24,000 and Constantius' at 30,000) lay on the field making this the bloodiest of all Roman battles. The Roman army was weakened beyond repair at a time when every man was needed to guard the frontiers against threats from barbarian tribes. Magnentius retreated to Aquileia, blocking the passes through the Julian Alps. Winter ended the campaign season but Constantius had shown no inclination to pursue Magnentius. Instead, he offered amnesty to any of Magnentius' followers who surrendered, except for those who were directly involved with his brother's murder. This caused many desertions from Magnentius' ranks. Magnentius renewed his offer to negotiate, but it was refused. Constantius sent letters to the barbarian tribes living along the Rhine with large donatives to encourage them to attack Magnentius. The barbarians were only too happy to invade Gaul, thereby keeping Decentius busy and removing much-needed troops from his brother's forces. This plan had an unfortunate aspect in that the barbarians devastated Gaul, destroying crops and causing towns and villages to be deserted. In August 352, Constantius' forces broke through into northern Italy and on September 26, 352, Constantius' nominee Naeratius Cerealis, a maternal uncle of Gallus, became praefectus urbi of Rome. By November, Magnentius had retreated to Gaul and Constantius was holding court in Milan. Magnentius could still count on his loyal Gauls for support and was able to piece together an army. In the spring or summer of 353, Constantius' army crossed the Cottian Alps into Gaul. Constantius and Magnentius fought one final battle at Mons Seleucus, and the usurper was decisively defeated. Trapped in Lugdunum (modern Lyon), Magnentius committed suicide by stabbing himself with his sword on August 11. Decentius, to whom Magnentius had sent an appeal for help, learned of his brother's death on the march at Sens, where he hanged himself on August 18.