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An Alternate History of the Roman Empire: The End of Constantine

By Tim Venning

A gold multiple of "Unconquered Constantine" with Sol Invictus.

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 fourteen articles this took us to 332. We join the story mid Constantine's reign as Emperor.

In 332 the Greeks of the Rome-allied Kingdom of Bosporus (in modern day Crimea) appealed to Constantine for aid against the Goths on the steppes to North. The Roman vassal Sarmatians (in Wallachia) would appeal to Constantine for help against raids by the Goths too. As a result, Constantine and his second surviving son Constantius, aged 20 and his designated heir to the East, crossed the Danube with a large army, and Sarmatian help, and marched North into the steppes as far as the Dniester River to defeat the Goths. Moreover, the Greeks of Bosporus attacked the Goths in the rear, aided by Roman troops who landed by sea at the mouth of the River Dnieper with heavy cavalry. As a result, the Goths surrendered and handed over hostages including the son of their leader, King Arian. They duly became Roman vassals and Constantine proclaimed himself as ‘Gothicus’ and celebrated a triumph on his return to his new capital, but they were not reliable allies and were soon plotting again in alliance with the Vandals to their West.

In 334 Constantine’s third surviving son Constans, then aged 17, was made “Caesar” and designated as the intended heir to a ‘central’ realm based on Italy, the upper Danube, and North Africa. This would include the old capital of Rome and the effective new Western capital of Mediolanum but he would still be junior in status to his elder brothers, Constantine II ruling at Trier and Constantius II ruling at Constantinople, a sign of shifting power away from Italy. Constantine’s half-brother Dalmatius, younger brother of Julius Constantius who had been consul in 331 and already had two sons by successive short-lived wives (Gallus and Julian), was serving as consul in 334. He then went to Antioch as “Censor” as the first step in Constantine’s plan to promote him as junior co-ruler to Constantine’s sons. Once they succeeded their father as ‘Augusti’, he would become ‘Caesar’ with authority over Syria and Mesopotamia – and the Emperor now began to conceive a plan to finish off his great predecessor Aurelian’s work as ‘Restitutor Orbis’ by defeating and breaking up Persia.

Under this ambitious scheme, all of Mesopotamia would be annexed as far as the Persian Gulf, vassal-states would be created in Media and Hyrcania, and Rome would dominate the land and sea routes to India along which trade flowed and become fabulously rich, taking the ‘Great King’s share of the Oriental trade for itself. Constantine would also create a separate principality in the North East of the Empire, carved out of the kingdom of Armenia, for Dalmatius’ son Hannibalianus. This would be expanded by annexed Persian lands in Atropatene and as far as the Caucasus, which would be seized in this final great Imperial expedition. Constantius II was sent to Antioch as the “Vicar” of the Eastern dioceses to prepare for the war; Constantine’s eldest son Constantine II was granted the ‘Vicarate’ of Britain, Gaul, and Spain and Constans that of Italy, Africa, and the upper Danube. But a surprise Gothic raid over the Danube on Lower Moesia – possibly due to stories that the Emperor was preoccupied with his Persian plans and would not retaliate – led to Constantine having to halt his Eastern plans for the moment and prepare an unwelcome new expedition North of the lower Danube.

Later that summer of 334 he campaigned over the Danube against the Goths and their Sarmatian allies with over 40,000 troops and a huge entourage, but the enemy retreated quickly across the Dneister and this time moved, with their supplies, out of range before the Imperial fleet could land the usual second force at the mouth of the Dnieper to catch them in the rear. Constantine ended up chasing them doggedly across the steppes nearly as far North as the middle Dneiper but, as his supplies began to run short, he lost his nerve and abandoned his camp to retire speedily to the sea. He was evacuated by ship from the mouth of the Dniester with his entourage while his generals marched or rode the main army back to the Danube along the coast in touch with the fleet, and though the impressive Roman heavy cavalry and their mobile catapults kept the Goths at a respectful distance the campaign had achieved nothing and could not be presented as a victory.

After this debacle, the Emperor abandoned his Northern plans. ‘Hit-and-run’ cavalry attacks across the nearer steppes would have to suffice for punishing the Goths and to avoid the risk of entrapment and defeat the unusually nervous Constantine now began to prefer buying off the Northern ‘barbarians’ rather than fighting them. Despite this, his Persian plans for a decisive campaign against a far more predictable and less versatile foe continued. In preparation for this, he would first move against internal foes.

In 335 he tried to silence the belligerent Bishop Athanasius by having him arrested and tried at Caesarea (Palestine), outside his see and so free from demonstrations in his favour, for magic practices and murder as alleged by the rival “Meletian” faction in Alexandria. But the bishop was acquitted again, this time after producing the local Egyptian bishop he'd been charged of murdering. As a result, the orthodox faction held onto the see of Alexandria. But their victory was short-lived as the adjoining Church administrative region of Palestine was full of bishops and their juniors who hated Athanasius for his criticisms of their supposed failings. They were thus more than ready to launch another legal enquiry and this time the over-confident Athanasius was caught making boastful statements that he was so popular that if the Emperor dared to arraign him he would call a strike of the Alexandrian dockers and cut off the grain-supply to Constantinople. This amounted to sedition, and he was soon on trial in Palestine again. This time he was found guilty and sacked as bishop, and a replacement – boycotted by most of the Alexandrian congregations – was installed in his cathedral early in 336. The Emperor also tried the tactic of putting pressure on the equally obdurate but politically weaker Arius to compromise and sign up to reunion with the official Church now Athanasius had been sent into exile. Unfortunately, after Arius was summoned to Constantiople for talks with the Emperor and his court clerics, amidst intense public interest as to whether he would compromise in his doctrine and pressure from his most fervent supporters not to do so, Arius collapsed and died suddenly before the religious ‘summit’ – reputedly in a public lavatory, or so his enemies alleged. His followers consecrated a successor as their bishop who refused to compromise, and so the stalemate continued.

Baptism of King Tiridates III of Armenia

Constantine had no more luck with Armenia. The famed great ruler Tiridates, who had adopted Christianity before Rome did, had died in 328 and his weaker son and successor King Chosroes accepted an invitation to Constantinople in July 335 and agreed to abdicate in Hannibalianus’ favour, in compensation he would receive Atropatene when it was conquered. But Chrosroes' countrymen were not so co-operative. News of his effective deposition in a Roman prince’s favour reached the capital, Artaxata, before Hannibalianus (based at Trapezous in Pontus) and a Roman army did, and the prince arrived to find that a cousin of Chosroes’ called Diran had been raised to the throne by a nationalist revolt and the local Roman garrison was under siege. The Romans besieged but failed to take Artaxata, and as a Persian army summoned by rebellious nobles approached Hannibalianus had to retreat and be content for the moment with the western third of Armenia.

The Emperor, who had just lost his half-brother Dalmatius (Hannibalianus’ father) and had had to replace him at Antioch with his other son the younger Dalmatius, had to raise his planned army for the Persian war earlier than intended, and in spring 336 he led a huge force as far East as Caesarea-in-Cappadocia with his son Constantius II in attendance. The future ruler of the East then achieved his first military success with a march to and the capture of Artaxata and during the rest of 336 most of Armenia was reduced and was duly handed over to Hannibalianus, but the planned arrival of a large force of Alans hired from the NE steppes via the Darial Pass in the Kur valley to head on into Atropatene did not occur due to an unexpected war between rival Alan factions on the steppes and a mutiny in the Emperor’s Arab-led camel corps on Cyprus as they practiced for their planned march on Ctesiphon required the diversion of troops there.

(Divergence from OTL: in reality Constantine died in May 337 and the planned for campaign against Persia was abandoned entirely. This article will try and sketch out what that campaign would look like were it to happen.)

In spring 337, the Emperor returned from a winter in Constantinople to Antioch to lead his men onto the Mesopotamian plains with a huge army 50,000 strong, protected by Roman and Arab cavalry from ambush. En route he ordered the sacking of the ultra-orthodox Church polemicist Bishop Marcellus of Ancyra, an ally of Athanasius and foe of Arius, for violent polemics about the Arians and the ‘heretic’ sect of ‘Origenists’ in order to mollify the latter and coax them back into the Church. However, taking Ctesiphon when the outnumbered Persians retreated into the Zagros was no substitute for having the adherence of enough Persian princes or nobles to start up a civil war, as Aurelian had found in 276-7 and Constantine was to find here. Moreover, when the Emperor fell ill in the summer heat at Ctesiphon he had to hurry back up the Euphrates to Syria and leave the war to his son Constantius.

Meanwhile Hannibalianus had been assassinated in Armenia in an ambush; rumour had it that disquiet among traditionalists among his officers at a Roman prince taking the ‘unlucky’ title of King had led to a plot by his own men, possibly backed by his jealous cousin Constantius. So the Emperor both had to divert troops from Persia to fight the rebls in Armenia and agree to Chosroes returning as his vassal-king. As a result a second advance by the Emperor into lower Mesopotamia in 338 was no more successful except that he reached Charax. A treaty had to be patched up with Persia and Rome’s sole gain was a small salient of fortresses on the upper Tigris North East of Nisibis. The loyal local noble installed in 338 as vassal-king of Atropatene was allowed to keep his throne by ‘Great King’ Shapur (but was quietly murdered later), and Constantine had to reluctantly accept that Armenia was safer under a local ruler of its ancient royal family than one of his own dynasty. His great ambitions in the east had, like that of many Roman Emperors before him, amounted to little in reality.

Bust of the Sasanian king Shapur II, who remains secure in his control in this timeline

Constantine also still wished to restore Church unity as the mutual vitriol of the orthodox upholders of the theology set out as ‘official’ at Nicaea and the Arians was increasing by the month. He identified the orthodox as the more obdurate though their men had more influence at his court and could argue that they, unlike the Arians, were loyal to his vision and were willing to obey his orders. The deposed and exiled Athanasius was in Palestine stirring up the militant ‘Nicaeans’ who were moving into the new shrines there as priests and other officials to refuse to deal with any dissidents, and was arguing that failing to impose unity would bring God’s wrath on the Church and was betraying all that the martyrs of the 300s had died for. Unimpressed, Constantine had Athanasius deported to a remote area of eastern Asia Minor, imposed a more forceful new Patriarch in Jerusalem with orders to sack clergy who refused communion to all but the most violent Arians, and ordered the Empire’s clergy to be more charitable to each other – and was mostly ignored. In May 340, Constantine fell ill on a tour in Bithynia, received baptism from Bishop Eusebius of Nicomedia (by now his closest religious adviser despite hid doubtful orthodoxy and semi-secret patronage for Arian clerics) at Helenopolis as his condition deteriorated, and died at a nearby village aged 66 or 67.

His body was returned to Constantinople; his sons joined an assembly of the leadership in the capital for the funeral, while in the interregnum Constantine was treated as still the legal head of State; Bishop Eusebius became involved in a plot against Constantine’s half-brother Julius Constantius and nephew Dalmatius and spread rumours of their doubtful orthodoxy and hostile intentions towards the late Emperor’s sons. Though in fact as an Arian sympathizer he had hopes from the equally religiously heterodox Constantius II of jobs and toleration for the Arians under his rule and the two of them feared Julius Constantius’ dislike for the Arians and were out to ‘smear’ him.

Constantine was buried in the cathedral of the Holy Apostles at Constantinople, but his sons resisted Dalmatius’ claim to a promise of the lower Danube from the late Emperor as his ‘Caesarship’ in 339 and the prospect of Julius Constantius demanding lands too at their expense. A few days later Imperial guardsmen rioted and murdered Dalmatius and his uncle Julius Constantius (and the latter’s eldest son) together with some sympathetic ministers, probably at Constantius’ initiative - the sons of Constantine were now left sole heirs. Julius’ younger sons Gallus and Julian, both aged under ten so unable to rule, were hidden in a church and were spared – possibly against the ruthless Constantius’ original intentions and at the demand of his clerics. On 9 September 340 Constantine’s sons agreed to a division of Empire in a meeting at Viminiacum in Illyricum – as their father had planned, Constantine II would have the far West, Constans would have Italy, North Africa, and the upper Danube, and Constantius II would have the East. Constantius sent his under-age rivals away from court and hopefully away from any intrigue on their behalf - Gallus to school at Tralles, and Julian to Nicomedia under the guardianship of his ally Bishop Eusebius. The Imperial trio in power now proclaimed their late father ‘the Great’ and vowed to keep up his work, but they were soon to prove themselves not to share his talents or dedication to justice and unity – just his suspicious nature and love of adulation.

Large statue of Constantine II. Photo taken by Wikimedia user 'TcfkaPanairjdde ' and shared under the CC BY-SA 3.0 licence.

Athanasius now returned to Alexandria and Marcellus to Ancyra with the acceptance of the three brother Emperors, but they were refused entry by opponents led by Arians and set off for the orthodox-dominated West with other expelled anti-Arian Bishops. Bishop Julius of Rome publicly accepted their orthodoxy and admitted them to communion.

In 341 Constantius had to progress East for military manoeuvres at Callinicum on the Euphrates to overawe Persia into keeping the peace, and also received and paid due courtesy to his client-king Chosroes of Armenia to keep him loyal and make sure he turned down Persian offers of money and troops if he revolted. Though he was as determined at enforcing obedience in politics and as rigorous a centraliser as his father, Constantius lacked his military expertise or confidence and so wished to avoid war. Especially as his cost-counting bureaucrat allies at the capital advised him that a war would be costly and new taxes could stir up dissent and cause his subjects to call in one of his more militarily enthusiastic brothers to overthrow him. He was also as determined to sort out the internal feuds of the Church as his father, but from the standpoint of a man who was increasingly sympathetic to Arianism and was not convinced of Christ’s eternal divinity – probably persuaded by his close friend and confidante Bishop Eusebius who became his closest Church adviser.

It seems to have been Eusebius who persuaded him, as a Northern equivalent of his pacifistic policy towards Persia, not to risk a glory-seeking clash with the Goths in case they retreated out of range across the steppes and humiliated him as they had done to his father in 334. Eusebius argued it would be wiser to convert them to Christianity and make their kings his loyal bribed vassals who would supply his armies with troops and his raid-denuded Lower Danube farms with tax-paying farmers – and additionally Constantius would win God’s praise by avoiding bloodshed. Accordingly, in the early 340s a missionary cleric called Ulfilas, half-German by birth and with relatives in Gothic territory, was employed on a mission to the Goths to start converting their nobility, accompanying a diplomatic mission to ‘king’ Araric in the Dniester valley (who was to receive Roman gifts and titles as a vassal) and then converting him and his elite. The success of this led to more Gothic-speaking missionaries being despatched from the Church in Constantinople there in 344 and 346. After a visit to Palestine to tour the Holy Places and show his devotion by lavishing gifts on the major shrines, Constantius returned to Constantinople later in 342 to sort out a disputed election of the new Bishop, sacked the hard-line ‘Nicaean’ Paul, and installed Macedonius who was a protégé of Eusebius and duly removed assorted anti-Arian clerics and administrators to bring in Arians. This was part of the Emperor’s and Eusebius’ plan to ‘fix’ Church appointments in Asia Minor and the Balkans in favour of Arians and marginalise those ‘Nicaeans’, or Catholics, who would not co-operate – but it only led to hard-line Nicaeans fleeing to the West to seek the support of ‘Catholic’ Bishop/ ‘Pope’ (meaning ‘Father’, that is ‘Holy Father’) Julius in Rome .

Julius was being stirred up against Constantius and his ‘heretic’ adviser Eusebius by the militant Athanasius, and though the local Emperor Constans was a hunting-mad hedonist who did not share Constantius’ interest in theology he was ambitious and soon saw the attractions of using the angry Catholics to undermine his brother. The vain and scheming Constans had initially been focused on overthrowing his eldest brother Constantine II, who despite being the eldest of the three brothers was the weakest and lacked his father’s ‘drive’ or political ability. Vain, charming, and militarily capable but preferring alcohol and hunting to war let alone politics, Constantine II had left the ‘lead’ in eliminating their uncle Julius Constantius to the more ruthless Constantius in 340 and now he ignored the intrigues against him at Constans’ court. Instead his attention was on his North West frontier, showing off his military ability and winning plaudits for a campaign to force vassalage and hostages out of the Franks and their Alemanni allies in 342 in a march to the Elbe. In practice Constantine was a political puppet of his chief adviser, the cunning Praetorian Praefect Ablabius, a scheming and efficient but brutal ‘hard man’ administrator who the first Constantine had not fully trusted due to his lack of morals or justice and had sidelined in the mid-320s. He'd had his rank and power restored by his effective service to Constantine II at Trier in the 330s and been Praetorian Praefect there since 335.

It was Ablabius (in OTL dead by this point) who protected his master’s security and in 343 uncovered a military mutiny plot on the upper Rhine which was apparently intended to hand the region over to Constans – and he persuaded his master that this was to have been the first part of a master-plan by Constans and his scheming local ‘duces’ to take over the entire Rhineland and then depose and kill Constantine. The alarmed Emperor was persuaded to strike first to save his throne and in April 344 suddenly turned a military rendezvous at Argentoratum (Strasbourg) from a supposed campaign against the Alemanni into a march via Helvetia towards Italy to try to catch Constans unaware at Mediolanum while most of his army was fighting a German invasion of Marcomannia. But the plan failed; Constantine II, aged 32, was assassinated by a mystery archer in a wood in central Helvetia while riding at the head of his army towards the Brenner Pass and his leaderless army had to halt and negotiate terms with Constans instead. As the army in Marcomannia was hurrying South, they abandoned any idea of raising one of their generals to the throne and fighting and recognized Constans as Emperor instead in return for an amnesty – and Constans succeeded to the role of Emperor of all the West. Ablabius and his ‘hard-line’ allies at the court in Trier attempted to flee but were rounded up and executed. It was never clear if Constans had been tipped off about the plan to attack his realm in time and sent assassins to kill his brother and hold up the attack or if this was a local initiative by officials or officers who were enemies of Ablabius and did not want him running the central Empire’s administration.

(Some divergences from OTL here; Constantine II was killed invading Italy in 340 not 344 in reality, and Constans then ruled all the West until his assassination in 350.)


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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