The Battle of Mons Seleucus was fought in 353 between the forces of the Roman emperor

Constantius II Constantius II (Latin: ''Flavius Julius Constantius''; grc-gre, Κωνστάντιος; 7 August 317 – 3 November 361) was Roman emperor from 337 to 361. His reign saw constant warfare on the borders against the Sasanian Empire and Germanic ...

and the forces of the usurper

Magnentius Magnus Magnentius ( 303 – 11 August 353) was a Roman general and usurper against Constantius II from 350 to 353. Of Germanic descent, Magnentius served with distinction in Gaul under the Western emperor Constans. On 18 January 350 Magnentius ...

. Constantius' forces were victorious, and Magnentius later committed suicide.

Background

Following his defeat at

Mursa Osijek () is the fourth-largest city in Croatia, with a population of 96,848 in 2021. It is the largest city and the economic and cultural centre of the eastern Croatian region of Slavonia, as well as the administrative centre of Osijek-Baranja ...

, Magnentius fled to Aquileia. This campaign included summoning all those loyal to him to support him in Aquileia.

Decentius Magnus Decentius (died 18 August 353) was ''caesar'' of the Western Roman Empire from 350 to 353, under his brother Magnentius. History Nothing is known of Decentius prior to 350. Magnentius usurped power from Constans on 18 January 350, and ...

, brother of Magnentius and newly made Caesar, was engaged with an incursion of Alemanni, and was unable to lend his army to support Magnentius. Constantius spent his time recruiting troops and retaking towns occupied by Magnentius. In the summer of 352, Constantius moved into Italy, only to find that Magnentius had chosen not to defend the peninsula.

Battle

The armies met at Mons Seleucus, in what is now La Bâtie-Montsaléon in Hautes-Alpes, south-eastern France. Constantius was again victorious and Magnentius took his own life on 10 August 353. Following his conclusive battle, Constantius wintered his troops at Arles.

Aftermath

Constantius, now undisputed Emperor of the Roman Empire, appointed Julian ''Caesar'' over the western half of the Empire in 355/6, and instigated a campaign to persecute those who had supported Magnentius. According to

Ammianus Marcellinus Ammianus Marcellinus (occasionally anglicised as Ammian) (born , died 400) was a Roman soldier and historian who wrote the penultimate major historical account surviving from antiquity (preceding Procopius). His work, known as the ''Res Gestae ...

, Constantius had become more "cruel, violent, and suspicious with age", and his ''notarii'' and bodyguards needed no pretext beyond mere suspicion to inflict punishment.

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* * * * 353 Mons Seleucus 353 Mons Seleucus 353 350s in the Roman Empire Mons Seleucus Hautes-Alpes Mons Seleucus Constantius II {{AncientRome-battle-stub