Flavius Magnus Magnentius
Roman Emperor of the West (350-353)

Magnentius was born about the year 303 in the town of Samarobriva (modern Amiens) in Gaul of a British father and a Frankish mother. Despite his 'barbarian' origins, Magnentius joined the Roman army; marking a trend that was to become evident throughout the fourth century when so-called barbarians began taking an increasingly greater role within the Roman army. He began his military career under the rule of Constantine and rose through the ranks, and he was eventually appointed as the comes or commander of the elite legions, the Joviani and the Herculiani.

After the death of Constantine on the 22nd May 337 the empire was divided between his three sons, Constantine II, Constantius II and Constans. In the year 340 Constans eliminated his brother Constantine II and brought the whole of the Western Roman Empire under his control. Constans however, became an unpopular and disliked ruler; he was active in his persecution of the Donatists in Africa as well as the pagans and the Jews; there were accusations of tyrannical behaviour and favouritism, the sale of government posts to the highest bidder as well as condemnation of his nocturnal activities with young men.

Magnentius was by then one of Constans' senior generals and obviously aware of his master's unpopularity. By the end of the year 349, perhaps encouraged by news of the military setbacks Constantius was suffering in the east, and with the belief that the army in the west would support him, he decided to rebel and seek to overthrow Constans from power.

In this he seems to have been assisted by one Marcellinus, described by Edward Gibbon as the "author of the conspiracy" and who was, as it happens, Constans' finance minister and therefore had access to the imperial treasury. (A key advantage in any revolt as it funded the payment of bribes often necessary to convince the reluctant to change sides.)

In order to launch the rebellion the two stage managed an event at Augustodunum 1 on the 18th January 350 when Marcellinus held a party and invited the aristocracy of Gaul to celebrate his son's birthday. There Magnentius appeared at an opportune moment wearing the imperial diadem and purple, was acclaimed augustus, at which point Marcellinus ensured that the appropriate oaths of loyalty were extracted from those present. Augustodunum was soon under the control of the conspirators and the army in Gaul and Britain rapidly declared their support.

As soon as Constans learned of the revolt and the defection of the army he decided to flee from Italy to Spain. Magnentius sent one of his henchmen named Gaiso after him. In the February of 350, Gaiso caught up with Constans at a town called Helena, in the Pyrenees, dragged him from the temple in which he was vainly seeking refuge and killed him.

At the time Constantius II was far too occupied with matters in the east, specifically fighting Persia, to react immediately to the overthrow and death of his brother, and the only practical opposition to Magnentius came from one of Constantius' cousins, named Julius Nepotian.

On the 3rd June 350 this Julius Nepotian 2 declared himself emperor at Rome and with the support of an armed band of gladiators and slaves, defeated a force led by the praetorian prefect Anicetus and seized control of the senate. Twenty-eight days later however on the 30th June, Marcellinus appeared with a force to crush the revolt on behalf of Magnentius. Julius Nepotian was killed, and his head placed on a spear and paraded around Rome.

For good measure, Nepotian's mother Eutropia was also killed as were any remaining relatives and supporters the conspirators could get their hands on.

Magnentius, Constantius II and Vetranio

With the unpopular Constans and his family now removed from the scene, the whole of the west including all of Gaul, Britain, Africa, and Spain was firmly in the hands of Magnentius.

There remained the question of whether the legions on the Danube would decide to support the usurper Magnentius or the eastern emperor Constantius II. In the event they decided on their own candidate in one Vetranio. It seems that Constantius' sister Constantina was instrumental in persuading Vetranio to accept this particular honour and it seems likely that she was pursuing her own agenda in this respect.3

Meanwhile, Magnentius send representatives to meet Constantius at Heraclea in Thrace and offered terms by which he, Magnentius, would be allowed to retain control of the west - a marriage alliance was proposed with Magnentius to marry Constantina whilst Constantius would wed the daughter of Magnentius. Constantius rejected these overtures, claiming that he had experienced a vision whereby his father had appeared and called on him to exact revenge for his brother's death.

Constantius also rejected the claims of Vetranio as co-ruler and whilst Vetranio briefly flirted with the idea of an alliance with Magnentius, he had no stomach for conflict and when Constantius and he met at Sardica 4 on the 25th December 350, Vetranio meekly handed over control of the Danube legions to Constantius and retired from public life.

It was therefore clear to all parties at the close of 350 that war was inevitable, and the necessary preparations were made; Magnentius appointed his brother Flavius Magnus Decentius as caesar and entrusted him with the defence of Gaul and the Rhine frontier, whilst Constantius in turn, elevated his cousin Gallus to the same rank to take charge in the east. Constantius rapidly concluded his war with Persia and made a quick peace treaty so he could gather his forces to face this new threat from the west.

Civil War 351-353

In the year 351 the war between Constantius II and Magnentius began. Magnentius gathered together a large army by withdrawing a number of legions from the defence of the Rhine frontier and hiring German mercenary troops to bolster the numbers.

Constantius moved first and tried to invade Italy but was defeated at Atrans 5 and was forced to withdraw. As Constantius retreated, Magnentius followed seeking to confirm his initial advantage. The two forces clashed at the Battle of Mursa, where Magnentius was utterly defeated, in what was to be acknowledged as the bloodiest battle of the fourth century, with a total of 50,000 killed.

Magnentius fled back to Italy and sought once again to reach a settlement with Constantius whilst he tried to build another army. But Constantius rejected him once again and in the summer of 352 invaded Italy, forcing Magnentius to retreat to Gaul.

Magnentius made an attempt to assassinate Gallus, in the hopes that the death of his ceasar back in the east would force Constantius to abandon his invasion but this all came to nothing. Constantius eventually moved into Gaul in the late summer of 353 and on the 11th August inflicted a crushing defeat on Magnentius at the battle of Mons Seleucus.

Magnentius retreated with his few remaining troops to the relative safety of Lugdunum (modern Lyons), but with the Germans, encouraged by Constantius, also rampaging through Gaul and his troops now openly declaring their support for his rival, it was clear to Magnentius that it was all over. Rather than be handed over to face Constantius retribution, Magnentius fell on his sword and ended his own life. His brother Decentius likewise hanged himself at Senonae after receiving the news of Magnentius' death.

The aftermath of the revolt

Not a great deal is known of Magnentius himself, particularly as Book 13 of Ammianus Marcellinus work Res Gestae Divi Augustae, that would have covered his reign as well as possibly his previous life and career is missing. The future emperor Julian in his Panegyrics for Constantius was careful to accuse Magnentius of various acts of wanton cruelty and the historian Aurelius Victor described him as "savage in character, as one would expect in a barbarian"6, although these remarks may reflect more on contemporary Roman prejudice rather than an accurate assessment of character.

It does appear that Magnentius was a pagan, which may well have been a source of additional provocation to the Christian Constantius. His paganism did not stop Magnentius from issuing coins with a large Chi-Rho symbol, no doubt in a bid to placate the growing Christian faction within the empire. Despite this it seems that Magnentius drew a great deal of support from the pagan community as he was naturally, disinclined to continue with the persecutions of his predecessors.

In the aftermath of Magnentius' defeat Constantius naturally insisted on the execution of the surviving leaders of the regime and an active investigation identifying those who had supported the revolt.

It seems as if many in Britain, perhaps due the family connections Magnentius had with the island, was active in their support for the revolt, as it was there that Constantius sent one Paulus Catena to root out the remains of the conspiracy. Paulus Catena was indiscriminate with his accusations of treason and ruthless in exacting the resulting penalties.

When the vicarius of Britannia, Flavius Martinus expressed his opposition to Paulus Catena methods and results, this was interpreted as evidence of his own guilt and he was forced to commit suicide. The witch hunt therefore continued unabated where; The most innocent subjects of the West were exposed to exile and confiscation, to death and torture according to Gibbon. There also appears to have been a religious dimension to the persecution as there was also an attack on pagan monuments and practices that had previously been allowed by Magnentius but where now seen as irrevocably linked to the taint of treason.

The reign of terror instigated by Paulus Catena made a lasting impression on the contemporary British psyche; the approval of his actions by the Roman authorities did much to undermine support for the Empire. Magnentius' revolt may have failed, but in his homeland it precipitated a change of events that would ultimately lead to the final break between Britain and the Empire.


1 Augustodunum or modern Autun in France.

2 Julius Nepotian sometimes known as Nepotianus who was the son of Eutropia, a sister of Constantine and therefore Constantius' aunt.

3 Constantina who was technically Augusta and therefore empress in her own right, may well have been seeking her own proxy through which she could exercise authority.

4 Sardica is modern Sofia in Bulgaria.

5 Atrans is modern Trojane in Slovenia.

6 From the Liber de Caesaribus of Sextus Aurelius Victor.


Resources on Magnentius :-

David A. Wend - Coinage Overview at http://www.geocities.com/Athens/Parthenon/7094/magn3.html

Edward Gibbon The History of the Decline and Fall of the Roman Empire - Chapter XVIII: Character of Constantine and his Sons. Part IV.

P Salway Roman Britain (OUP, 1991)