Editing Constantius II (section)

== Augustus in the east ==
[[File:Impero_Romano_da_maggio_a_settembre_337.png|thumb|alt=|200x200px|Division of the Roman Empire among the ''caesares'' appointed by [[Constantine the Great]], before the death of [[Dalmatius]]]]
[[File:Colossal Portrait or Constantius II or Constans.jpg|thumb|upright|alt=|Bust of youthful Constantius II or Constans, [[Capitoline Museums]]<ref>[https://www.museicapitolini.org/en/opera/testa-colossale-di-costanzo-ii-o-costante Constanzo II o Constante]. ''Musei Capitolini''</ref>]]
[[File:Double Centenionalis Magnentius-XR-s4017.jpg|thumb|alt=|Bronze coin of [[Magnentius]]]]
[[File:Solidus-Constantius Gallus-thessalonica RIC 149.jpg|thumb|alt=|Gold solidus of [[Constantius Gallus]]. A paternal cousin of Constantius, he was made [[Caesar (title)|Caesar]] by Constantius in 350 and was married to the [[Roman emperor|emperor]]'s sister, [[Constantina]]. However, his mismanagement of the eastern provinces led to his death in 354.]]

In early 337, Constantius hurried to [[Constantinople]] after receiving news that his father was near death. After Constantine died, Constantius buried him with lavish ceremony in the [[Church of the Holy Apostles]].{{sfn|Hunt|1998|p=1}} Soon after his father's death, the army massacred his relatives descended from the marriage of his paternal grandfather [[Constantius Chlorus]] to [[Flavia Maximiana Theodora]], though the details are unclear.{{sfn|Burgess|2008|p=10}}{{sfn|Hunt|1998|p=3}} Two of Constantius's uncles ([[Julius Constantius]] and [[Flavius Dalmatius]]) and seven of his cousins were killed,<ref name="Letter">Julian, "Letter to the senate and people of Athens", 270. {{Wikisource-inline|Letter to the senate and people of Athens|single=true}}</ref> including [[Hannibalianus]] and [[Dalmatius]], rulers of [[Diocese of Pontus|Pontus]] and [[Diocese of Moesia|Moesia]] respectively, leaving Constantius, his two brothers [[Constantine II (emperor)|Constantine II]] and [[Constans]], and three cousins [[Constantius Gallus|Gallus]], [[Julian the Apostate|Julian]] and [[Nepotianus]] as the only surviving male relatives of Constantine the Great. While the “official version” was that Constantius's relatives were merely the victims of a mutinous army,{{sfn|Burgess|2008|p=25}}<ref name="ReferenceA">[[Eutropius (historian)|Eutropius]], ''Historiae Romanae Breviarium'' X.9</ref><ref>Julian, "Letter to the senate and people of Athens", 271. {{Wikisource-inline|Letter to the senate and people of Athens|single=true}}</ref>  [[Ammianus Marcellinus]], [[Zosimus (historian)|Zosimus]], [[Libanius]], [[Athanasius of Alexandria|Athanasius]] and Julian all blamed Constantius for the event.{{sfn|DiMaio|1992|p=165}}<ref name="Letter"/> Burgess considered the latter version to be “consistent with all the evidence”, pointing to multiple factors that he believed lined up with the massacre being a planned attack rather than a spontaneous mutiny - the lack of high-profile punishments as a response, the sparing of all women, the attempted [[damnatio memoriae]] on the deceased, and the exile of the survivors Gallus and Julian.{{sfn|Burgess|2008|pp=26–27}}{{efn|By 351–354, Constantius’s courtiers stopped denying his involvement and instead claimed he was tormented with guilt over his role in the massacre.<ref name="Letter"/>{{sfn|Burgess|2008|pp=16–17}}}}

Soon after, Constantius met his brothers in [[Pannonia]] at [[Sirmium]] to formalize the partition of the empire.{{sfn|Hunt|1998|p=4}} Constantius received the eastern provinces, including Constantinople, [[Roman Thrace|Thrace]], [[Asia Minor]], [[Roman Syria|Syria]], [[Roman Egypt|Egypt]], and [[Cyrenaica]]; Constantine received [[Roman Britain|Britannia]], [[Roman Gaul|Gaul]], [[Hispania]], and [[Mauretania Tingitana|Mauretania]]; and Constans, initially under the supervision of Constantine II, received [[Italia (Roman Empire)|Italy]], [[Africa Province|Africa]], [[Illyricum (Roman province)|Illyricum]], [[Pannonia]], [[Macedonia (Roman province)|Macedonia]], and [[Achaea (Roman province)|Achaea]].{{sfn|Hunt|1998|p=4}}

Constantius then hurried east to [[Antioch]] to resume the [[Perso-Roman wars of 337–361|war with Persia]].{{sfn|Hunt|1998|pp=11-12}}<ref name="autogenerated1">Theodoret, ''Historia Ecclesiastica'' II, 30, 1–14, GCS</ref> While Constantius was away from the eastern frontier in early 337, King [[Shapur II]] assembled a large army, which included war elephants, and launched an attack on Roman territory, laying waste to Mesopotamia and putting the city of Nisibis under siege.{{sfn|Hunt|1998|p=12}} Despite initial success, Shapur lifted his siege after his army missed an opportunity to exploit a collapsed wall.<ref name="autogenerated1"/> When Constantius learned of Shapur's withdrawal from Roman territory, he prepared his army for a counter-attack.

Constantius repeatedly defended the eastern border against invasions by the [[Sassanid Empire]] under Shapur. These conflicts were mainly limited to Sassanid sieges of the major fortresses of [[Roman Mesopotamia]], including [[Nisibis]] ([[Nusaybin]]), [[Singara]], and [[Diyarbakir|Amida]] ([[Diyarbakir]]).{{sfn|Hunt|1998|p=13}} Although Shapur seems to have been victorious in most of these confrontations, the Sassanids were able to achieve little.<ref name="ReferenceB">[[Festus (historian)|Festus]], ''Brevarium'' XXVII</ref>{{sfn|Dingas|Winter|2007|p=89}} However, the Romans won a decisive victory at the Battle of Narasara, killing Shapur's brother, Narses.{{sfn|Hunt|1998|p=13}} Ultimately, Constantius was able to push back the invasion, and Shapur failed to make any significant gains.{{sfn|Dingas|Winter|2007|p=89}}

Meanwhile, Constantine II desired to retain control of Constans's realm, leading the brothers into open conflict. Constantine was killed in 340 near [[Aquileia]] during an ambush.{{sfn|Hunt|1998|p=5}}{{sfn|Drinkwater|2007|p=199}}{{sfn|Crawford|2016|p=64}} As a result, Constans took control of his deceased brother's realms and became sole ruler of the Western two-thirds of the empire. This division lasted until January 350, when Constans was assassinated by forces loyal to the [[Roman usurper|usurper]] [[Magnentius]].{{sfn|Hunt|1998|p=11}}{{sfn|Potter|2004|p=471}}{{sfn|Crawford|2016|p=72}}

===War against Magnentius===
{{main|Roman civil war of 350–353}}
Constantius was determined to march west to fight the usurper.{{sfn|Errington|2006|p=16}} However, feeling that the east still required some sort of imperial presence, he elevated his cousin [[Constantius Gallus]] to ''caesar'' of the eastern provinces.{{sfn|Barnes|1993|p=105}}{{sfn|Potter|2004|p=472}} As an extra measure to ensure the loyalty of his cousin, he married the elder of his two sisters, [[Constantina]], to him.{{sfn|Hunt|1998|p=17}}

Before facing Magnentius, Constantius first came to terms with [[Vetranio]], a loyal general in [[Illyricum (Roman province)|Illyricum]] who had recently been acclaimed emperor by his soldiers.{{sfn|Barnes|1993|p=101}} Vetranio immediately sent letters to Constantius pledging his loyalty, which Constantius may have accepted simply in order to stop Magnentius from gaining more support. These events may have been spurred by the action of Constantina, who had since traveled east to marry Gallus. Constantius subsequently sent Vetranio the imperial diadem and acknowledged the general's new position as ''augustus''.{{sfn|Potter|2004|p=472}} However, when Constantius arrived, Vetranio willingly resigned his position and accepted Constantius's offer of a comfortable retirement in [[Bithynia]].{{sfn|Hunt|1998|pp=16–17}}

In 351, Constantius clashed with Magnentius in [[Pannonia]] with a large army. The ensuing [[Battle of Mursa Major]] was one of the largest and bloodiest battles ever between two Roman armies.{{sfn|Potter|2004|p=473}}{{sfn|Hunt|1998|p=20}} The result was a victory for Constantius, but a costly one. Magnentius survived the battle and, determined to fight on, withdrew into northern Italy. Rather than pursuing his opponent, however, Constantius turned his attention to securing the Danubian border, where he spent the early months of 352 campaigning against the [[Sarmatians]] along the middle [[Danube]].{{sfn|Potter|2004|p=474}} After achieving his aims, Constantius advanced on Magnentius in Italy. This action led the cities of Italy to switch their allegiance to him and eject the usurper's garrisons. Again, Magnentius withdrew, this time to southern [[Roman Gaul|Gaul]].{{sfn|Potter|2004|p=474}}{{sfn|Barnes|1993|p=106}}

In 353, Constantius and Magnentius met for the final time at the [[Battle of Mons Seleucus]] in southern Gaul, and again Constantius emerged the victor.{{sfn|Potter|2004|p=474}} Magnentius, realizing the futility of continuing his position, committed suicide on 10 August 353.{{sfn|Hunt|1998|p=22}}{{sfn|Drinkwater|2007|p=201}}{{sfn|Barnes|1993|p=106}}