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An Alternate History of the Roman Empire: Constantius II - Paranoia in the Palace

By Tim Venning

This long Series of Articles discusses a hypothetical history of the Roman Empire wherein Marcus Aurelius lives longer and so it's more stable. In the first fifteen articles this took us to 345. We join the story with the Empire split between the rule of Constantius and his brother Constans.

Presumed bust of emperor Constantius II. Photo by 'Jebulon' who waved his rights of ownership.

In 345 a new ‘General Council of Western and Eastern Bishops' was called on by the two Emperors to assemble at Sardica/Sofia in Balkans to sort out the correct orthodoxy and the positions of Athanasius and of Marcellus of Ancyra. (Later than in OTL, when it was in 342/3.) The initiative was that of Constantius who hoped to win over the westerners to support a more tolerant approach to the Arians - and a share of posts in the western Church for them – by exposing the aggressive and insolent attitude of Athanasius and Marcellus, who were invited to attend too, to him and to the Imperial authority. These hard-line Catholics were implying that an Emperor who was not orthodox had betrayed Nicaea and betrayed the Church of Christ and should be defied; it could be presented as sedition and treason and even Constans should accept that. The westerners however had an almost united position in favour of orthodox ‘Catholicism’ and the creed formulated at Nicaea, as arranged by previous lobbying by Pope Julius and his growing bureaucracy in the Lateran Palace in Rome – and as agreed by Constans at his joining Julius in 344 for the inauguration of the completed Basilica of St Peter in the Vatican, as a means of embarrassing Constantius. The Council of Sardica/Sofia only led to deadlock between the eastern and western delegations, and it broke up as Western Bishops insisted on Athanasius and Marcellus of Ancyra participating as duly appointed and illegally deposed bishops and the Easterners refused. The latter, without their most forceful organiser Eusebius of Nicomedia who was absent doe to illness and in fact died a few weeks later, then withdrew and anathematized all concerned with defying their master Constantius’ wishes, and after that neither delegation would accept the others as legitimate or listen to what they had to say .

Two separate Councils in two separate parts of Serdica followed with embarrassed Imperial officials shuttling between the two sites to no avail, and the numerical - Western - majority led by Julius’ deputy and the bishops of Mediolanum and Bononia, close allies of Constans and probably under his orders, upheld Athanasius and Nicene orthodoxy. They issued a revised creed that could admit Marcellus (accused of “Sabellianism”) to communion along with some of the more moderate ‘Origenists’ and ‘Mellitans’ but not the Donatists or the Arians. The Eastern bishops condemned it and Constantius duly backed them and refused to accept the Westerners’ creed so he was declared an apostate and banned from issuing any religious decrees or making Church appointments that counted as legal in the West. The Western Church also anathematized the pro-Arian Bishop Valens of Mursa (North Illyria), the latest ecclesiastical adviser to Constantius who once Eusebius died became his closest ally and from 346/7 directed most of his – Arian –appointments in the Church. Constantine ‘the Great’s dream of a united Church was shattered and this became tied in with the growing mutual hostility of Constans and Constantius, each of whom used his Church to declare the other an apostate. Though this did not matter much directly in secular matters it encouraged exasperated senior bureaucrats and generals to regard the feuding Emperors as a disgrace to their father’s memory and some to hanker after the ‘might have been’ of the more tolerant and religiously ‘inclusive’ Julius Constantius and to look to the chances of his sidelined sons as better Emperors that the current pair, neither of whom had any sons even when they were aged over thirty.

To redeem his reputation and show his supposed military prowess, Constantius now reversed his pacifistic foreign policies to show more daring and aggression as it was felt his father’s son should do. First he marched troops into Armenia and on into Atropatene in 347 to impose a Roman client-king as a punishment on Persia for failing to pay ‘rent’ for some border fortresses on the upper Tigris as promised in 339. A year later, in 348, he also campaigned on the steppes North of the lower Danube to back up the Empire’s (Arian) Christianised Gothic allies by punishing their turbulent Herul and Vandal neighbours. The exercise of competent logistics to keep up food-supplies and the overwhelming superiority of Roman armoured cavalry over the lightly armed Germans kept the latter from tackling the nervous but publicly aggressive Emperor. So he was largely uncontested as he marched his army up the Dniester as far as Galicia and then on a ‘curve’ across Vandal territory South West to re-enter Roman territory at the Ostrava Gap, having secured loot, hostages, and treaties of vassalage that stabilised the frontier for a decade – and as ‘Vandalicus Maximus’ he could stage a Triumph in Constantinople later that year. Thousands of land-hungry and ambitious young Vandals and Heruls were invited to join the Roman army or come to settle as farmers in the lower Danube valley – which also boosted food-supplies for the frontier armies and tax-revenues – and the Emperor’s success also warned Constans off attacking him, which had seemed a possibility after the latter had campaigned successfully in Britain to push back a Pictish incursion into Lothian and as far as Hadrian’s Wall in 347.

Events now took an unexpected turn, avoiding the risk of a second civil war between Constantine’s fratricidal sons but threatening to start up the old round of revolt by non-dynastic contenders again. This was seen as ironic but disturbing by elite supporters of stability at court and in the bureaucracy – Diocletian had tried to avoid the danger of unworthy and incompetent heirs from within a dynasty by appointing heirs chosen on merit but failed, and now Constantine’s solution of ‘family rule’ was failing too. On the 18th of January 350 Marcellinus, the Count of Privy Purse (“Res Privatae”, court finance chief running the private Imperial expenses), and his clique of ministers and senior officers hailed a German general, Flavius Magnus Magnentius, aged 48 and possibly with a British parent, as Emperor. This happened during Flavius Magnus Magnentius's son’s birthday-party at the court winter residence at Augustodunum (Autun), Gaul, while Constans was out hunting. The troops joined in the revolt and Constans was killed in flight, aged only 33.

White statue of Constans

Magnentius, popular and capable and having won plaudits on the British campaign, was probably the compromise choice of a cabal of rebel ministers and generals. These elites were alarmed by the increasingly alcoholic and paranoid Emperor’s recent threats to purge his government of people who he feared were plotting with Constantius to remove him, and possibly Constans had heard rumours of a genuine plot. Alternatively, it might have been in his imagination or the rumours were the invention of his current clique of toadying senior aristocratic officers, mostly the sons of former leading 310s and 320s Constantinian generals. This clique wanted to secure more senior offices and money for themselves and were prodding the recently-divorced Emperor to marry again, to the daughter of one of his cronies who had already had two sons by her late husband so she was proven fertile.

Regardless of the reason for these threats by Constans, they allowed Magnentius to quickly secure control of the West, aided by his ambitious Arian wife Justina (a Cisalpine Gallic heiress with powerful noble allies at the court in Mediolanum, later to be married to Emperor Valentinian I) and Marcellinus. This was because most senior officials were disillusioned with the mercurial and lazy Constans who was seen as increasingly influenced in his choices of appointees by unworthy rakes. Magnentius sent senator Nunechius and ‘Magister Peditum’ Marcellinus to Constantius to obtain his support and hoped that his Arian wife and her links to Arian clerics in North Italy would reassure Constantius, but the Eastern Emperor put family solidarity first and refused to recognise him. He arrested the envoys, and marched West into the Balkans in a successful bid to rally the troops in Dacia and Marcomannia to back the dynasty of Constantine against the usurper, arguing that abandoning the dynasty that had brought the Christian religion to power would end the favour and victory that God had bestowed on the House of Constantine. Constantius sent his late father’s respected general Philippus as an envoy to Magnentius to both buy time and try to start a mutiny. The general pretended that he would accept the situation and secured Magnentius ‘ permission to address the troops at the new Imperial HQ at Lugdunum, but then rebuked them for their disloyalty and tried to get them to return to their allegiance to the House of Constantine. Magnentius hastily silenced him, but dared not arrest him lest this start a war. Philippus eventually told Magnentius that Constantius would let him rule Gaul and Britain, ie the realm of Constantine II, as junior Emperor if he handed Italy and North Africa over, but Magnentius refused the offer and detained him so he could not report on his army’s dispositions to Constantius.

The Rhine legions and Britain now came out in support of Magnentius, but the Imperial House’s old Frankish allies from Rhine to Elbe did not – possibly after receiving envoys with cash from the East – and as Constantius’ usefully-loyal Vandal vassals East of the River Oder sent a large mercenary force to Marcomannia to aid the pro-Constantius troops there a brief civil war in th province saw Magnentius’ allies, old military colleagues, chased out and fleeing to Rhaetia. Now Constantia, sister of Constantius and Constans and widow of Constantine I’s half-brother Hannibalianus, who was living in Illyricum, raised Marcus Vetranio, the governor of Illyricum based at Carnuntum, to the throne as her candidate – an unusual female ‘power-bid’ possibly aimed at getting revenge on Constantius for his rumoured part in her husband’s and his brother’s murders. But Vetranio refrained from fighting Constantius and assured him of his goodwill, and this pair appear to have reckoned that the son-less Eastern Emperor would need their military backing to avoid another fight that would weaken his troops ahead of their clash with Magnentius. The pro-Constantius forces now controlling Marcomannia , on orders from him or not, now agreed a truce with Vetranio and the latter lent them support to move troops into Rhaetia and western Noricum and secure these lands against Magnentius’ local backers, who had to flee.

On the 3rd of June 350 a further unexpected complication ensued to the civil war. Nepotianus (born 330), nephew of Constantine I and son of his half-sister Eutropia and the leading Roman senator and ex-consul Nepotius, a glamorous and popular officer-cadet of Imperial blood with plenty of family money to lavish on his supporters and a desire for a throne, led a revolt outside Rome to secure the local troops before it was known that Vetranio had revolted; at the time it was assumed that Constantius would be concentrating on Magnentius and the rule of Italy was ‘up for grabs’. He entered the old capital with his allies to evict Praetorian Praefect Anicetus who was a supporter of Constans but had offered his backing to Magnentius and been kept on. But Marcellinus had arrived a few days earlier at Mediolanum to take over the Imperial court there and bene backed by its troops, and he now headed South; on 10 July he entered Rome as the gates were opened by officers who saw resistance as hopeless and he restored Magnentius’ control of the city after fighting. Nepotianus and his mother Eutropia were among the killed, and Italy thereafter backed Magnentius. That autumn Constantius summoned his nephews Gallus (23) and Julian (19) from their Cappadocian exile to his court and HQ at Sirmium on the middle Danube to be sure of their loyalty and to, rather cynically given his past behavior, parade them as his heirs to reassure wavering soldiers and commanders that he was the candidate of dynastic stability and family unity among the House of Constantine. On 15 March 351 Gallus was elevated to be “Caesar” at Sirmium and sent to Antioch to govern the East , ‘controlled’ by ministers and officers who his cousin sent with him to keep an eye on his conduct and loyalty; Julian became a student at Ephesus where he was taught by the pagan philosopher Maximus and was duly influenced against Christianity to the future embarrassment of his Imperial patron.

In April 351 Constantius met Vetranio near Sirmium, both leaders with their armies in attendance in case of treachery, and by secret agreement when they met in front of their armies Vetranio announced his abdication and support for Constantius. His army joined Constantius, and the latter marched on Atrans near the Italian/Norican border but faced a larger army including the Rhine legions under Magnentius there and lost his nerve given the latter’s better reputation as a tactician who had a record for launching surprise attacks. He retreated East to wait for his Marcomannian troops and the German mercenaries to arrive; Magnentius advanced rapidly into Pannonia, forcing him to retreat further than intended, to seize Mursa. The two armies manoeuvred against each other and the Northern reinforcements joined Constantius to give him greater numbers; he offered Gaul and Britain to Magnentius, who was defeated in July 351 at the battle of at Mursa as his right wing was destroyed by Constantius’ cavalry. He retired to Italy and blocked the route into it at Aquileia; Bishop Valens of Mursa, having prayed publicly for Constantius’ victory and been joined by Constantius at a service during battle, joined him as he took over Noricum and Dalmatia and influenced him in favour of an Arian settlement of all the Church. Part of the Senate now defected from Italy to Constantius as the legal Emperor and heir of the old dynasty, also fearing a purge as Magnentius was short of cash after having to pay off the Franks from attacking the lower Rhine (most of his Rhine troops had been summoned to his side before the battle of Mursa) and he might be looking for people who had secretly backed Nepotianus as a source of cash if they were executed.

Golden coin depicting Magnentius facing right. Shared under CC BY-SA 2.5 licence.

Magnentius set up his base at Aquileia, and did his best to present himself as a conciliatory Western ruler who would not impose either Catholic or Arian beliefs on his clergy and was also more open to tolerating the pagans (still a majority of the population even in Italy, and especially so among the aristocracy in Rome despite Constantine’s 330 declaration of ‘tax-breaks’ for two years for those who converted). He was helped by the death of Athanasius’ anti-Arian patron Pope Julius of Rome in April 352 and made sure that a less confrontational cleric, the easy-going ex-socialite Latium aristocrat turned deacon Liberius, was elected to succeed him by the Roman clergy. The latter was attractive to the old capital’s clergy as a well-connected man with plenty of money who used his resources to host lavish religious ceremonies (with free food and religious processions) as an alternative attraction to the annual round of pagan rituals, and he persuaded many other aristocrats – women in particular – to convert too and give gifts to the Church; but Athanasius and Marcellus would not back him as he was not interested in anathematising Arians so they soon left Rome for more congenial hard-line clerical hospitality in Sicily,. In September 351, probably seduced by bribes smuggled into their barracks by long-term partisans of the family of Constantine I in the officer-corps, Magnentius’ main garrisons in N Italy revolted in his rear as Constantius’ fleet (sent from Thessalonica) landed at the mouth of the Po. He fled to Gaul, where his brother Decentius, his local ‘Magister Equitum’ left in charge of his troops at Trier, revolted against him and attempted to seize Trier. Constantius landed in Italy and secured Mediolanum, and Rome willingly defected to him in October as Magnentius’ cause there collapsed; also, to the North the Eastern troops in Rhaetia were able to head West to the upper Rhine and secure that region while its troops were absent helping Magnentius against Decentius in Belgica .

Magnentius defeated Decentius who fled into hiding , but the army of Lower Germania had broken up into pro- and anti-Decentius factions and had mostly left their riverine garrisons during the battle for Trier. The Germans, led by the Franks and Alemanni, poured across the undefended lower Rhine and ravaged the countryside of Belgica. In the East the turbulent and over-taxed minority Palestinian community of the Samaritans revolted around Lake Galilee in summer 352 but were brutally suppressed by Gallus in his first successful military campaign; their city of Sepphoris was sacked and he allowed his troops to get out of control as they looted it, making him popular with them but disturbing his ministers at Antioch who reported unfavourably on his quest for popularity with them to Constantius. In spring 353, as Constantius’ and Vetranio’s troops advanced down the Rhine to Moguntiacum and started to clear the Alemanni raiders out of the Vosges hills and forest where they were robbing farms and travellers, most of Gaul revolted against Magnentius who was struggling to hold onto his disintegrating army as Constantius marched through Provence to join a landing by his navy at Massilia and up the Rhone.

Ex-partisans of Constans among his former officers who had fled a desperate purge by Magnentius to try to intimidate his army emerged from hiding to attack his rear headquarters at Augustodum and seize his treasury there, and he was defeated by Constantius at Mount Seleucus in South West Gaul in mid-July as he retreated into Aquitaine. On 10th August he committed suicide in the hills of the Pyrenees after being trapped as he tried to flee to Spain; his officers then presented his head to Constantius on 6th September as he entered Burdigala. Most of them were pardoned and so was Justina who surrendered the imperial household at Augusta Senonorum (Sens) and was pardoned as an Arian co-religionist of Constantius, but the latter still faced trouble from elements of the disintegrating Lower Rhine army who turned bandit and he was unable to trust the officers who had treacherously deserted his brother for a non-dynastic ‘pretender’ in 350 and so many capable commanders ended up arrested and executed or flung into prison instead of being pardoned as was generally expected.

Constantius, always suspicious and ruthless, was slowly succumbing to paranoia and the fear that he would be abandoned and murdered as Constans had been, and his more crooked and devious courtiers and ministers started to play on this fear and encourage him to purge their personal rivals or to teach the rebel provinces of 350-3 – Gaul and Britain in particular as they had stood by Magnentius even when Constantius arrived with his army to ‘rescue’ them - a lesson, A thorough purge of disaffected civil and military elites would scare off future potential rebels, and it would also fill their own pockets as the victims’ estates and other possessions were confiscated and Constantius re-granted them to his own loyalists. Accordingly in 353-4 Constantius sent out teams of junior ministers and police officials to restore his rule to Magnentius’ provinces and round up suspects, particularly the brutal Paulus “The Chain”, a thuggish police official who terrorized the landed, military and administrative elites of Britain. Martinus, the arrested governor, tried to kill Paulus as he was dragged into court for his trial in Londinium and wounded him with a sword before killing himself, and the purge damaged the Emperor’s reputation permanently and led to seething discontent – as did the purge of Catholic secular and religious officials in favour of Arians which Constantius now ordered for Italy and soon for Gaul.

(Events in 350-3 similar to OTL, but the civil war is less serious and inter-Roman military losses are less so the Empire has stronger position to face German invasions later in decade.)


Timothy Venning is a respected Historian who won the London University History Prize in 1979 and whose latest straight history book is Cromwell's Failed State. He has also written multiple books of counter factual essays including Caesars of the Bosphorus, Eternal Caesars, King Charles or King Oliver and King Henry IX, all published by Sea Lion Press, and If Rome Hadn't Fallen.


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