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An Alternate History of the Roman Empire: Building for the Future

By Tim Venning

Constantius Chlorus

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 nine articles this took us to 293. We join the story mid Dicoletian's rule, during a British rebellion.

In summer 293, Diocletian arranged for a secure and orderly Imperial succession and extra help for the two ‘Augusti’ in wars by the appointment of two ‘Caesars’ as their assistants and eventual successors. As with the bureaucracy, a formal new system was created and the orderly-minded Emperor intended it to be permanent – though in fact there had been occasional ‘Caesars’ in office as deputy emperors and legally recognised heirs for decades, since Aelius Verus under Hadrian and Marcus Aurelius under Antoninus Pius. The rising Illyrian general Constantius ‘Chlorus’ (‘the Pale’), aged 44 (who in OTL would become Western Emperor) and already Maximian’s Praetorian Praefect, was adopted as ‘son’ and heir by Maximian in the West and had authority over Gaul and Britain, enabling Maximian to concentrate on the Rhine and Marcomannia while his new deputy dealt with Carausius; this led to Constantius setting up a new sub-capital and court and military HQ at Augusta Treverorum (Trier) and rumour had it that Maximian was not pleased that Diocletian had ignored his request to be able to name his own son, Maxentius, as ‘Caesar’ instead.

To be fair, Maxentius was only in his late teens and Diocletain wanted an older and more experienced ‘Caesar’; but it was his protégé, not Maximian’s, that now became heir to the West and so increased his grip on the region and some courtiers at Nicomedia hoped that the ambitious Maximian, who had lost out politically by failing to defeat Carausius, was on the way out . Diocletian himself adopted the slightly younger Galerius (An OTL Eastern Emperor born in the 250s), a peasant’s son from Upper Moesia, as his son and ‘Caesar’ for the East. On 1 June Constantius and Galerius assumed office in co-ordinated ceremonies in the West and East, at Trier and Nicomedia; Constantius either divorced (if he was legally married to her) or abandoned his current ‘wife’ Helena, daughter of an innkeeper from Naissus (Nis, Serbia), and married Maximian’s stepdaughter, Theodora; Galerius married Diocletian’s only child, his daughter by Prisca, Galeria Valeria (d 328). Constantius duly had three sons (Julius Constantius, Hannibalianus and Dalmatius) and three daughters by Theodora; Galerius and Galeria Valeria had a daughter who was engaged when a child to Maximian’s son Maxentius. Diocletian required Constantius’ son by Helena, Constantine, aged around twenty, to live at his court as effective hostage for his father’s loyalty.

Constantius used a new fleet to take control of the Gallic shores of the Channel later in summer 293, driving Carausius’ ships out of the river-mouths, and campaigned successfully to reduce his Frankish allies at the mouth of the Rhine to backing the Empire not the usurper. He then blockaded Gesoriacum in September and built a giant mole to block the mouth of the harbour to Carausius’ relief-fleet. Carausius failed to relieve Gesoriacum by sea from Dubris or take the mole, and retreated back toBritain; the port surrendered, just before the Channel tides smashed down the mole and freed the harbour-mouth. The Empire now ruled to the Channel coasts and Constantius could use his fleet as a proven success to operate in the local seas against Carausius’ shipping, banning European trade with Britain to hopefully induce the British elite and troops to desert their ruler, and setting the stage for invasion. Carausius was murdered a few weeks later by his finance-minister Allectus who became the new rebel Emperor of Britain, relying heavily on a force of Frankish mercenaries who had fled from Constantius’ attack on their homeland and were now employed to keep order as the British troops were increasingly unreliable. Assorted landowners who resented Allectus’ increased taxes ended up executed for ‘plotting’ and their property was given to the mercenaries , which did not make him any more popular, but he was an effective ruler and played up local fear of a harsh and centralising purge by a restored Empire if Constantius won (as Septimius Severus had imposed after he regained rebel Britain in 197).

In spring 296 Constantius’ main fleet sailed from Gesoriacum to invade Britain, but was driven back by bad weather apart from one squadron which landed in western Kent and besieged the naval headquarters at Dubris. Constantius then arrived with his main fleet to back up this force after the weather improved, and Allectus dared not fight his veterans but retired West leaving Dubris and Rutupiae to surrender with many naval officers and men still resenting the man who had killed their old commander Carausius and deserting nce the usurper’s feared Frankish bodyguard was out of the way. Simultaneously a second squadron under Gallic admiral Asclepiodotus, a veteran sailor used to the local tides and fogs, sailed from the mouth of the Senona (Seine), missed its rendezvous with Constantius in fog, and landed somewhere to the West on the South coast – probably on the Solent near Portus Adurni (Portchester) where Carausius had been building a new naval fortress for a squadron to patrol the middle Channel. The troops were uneasy at marching inland without Constantius’ force, so Asclepiodotus burned the ships to make them go on by ending hopes of re-embarking. They met Allectus’ army somewhere up the road towards Londinium and defeated them in battle, killing the usurper.

A coherent force of Allectus’ Frankish mercenaries escaped the battlefield and headed back to Londinium, intent on sacking it; fortunately that part of Constantius’ army which had landed first near Dubris and had been sent off NW after Constantius secured that fortress-depot were tipped off about what was happening and arrived there before them to rescue the city and defeat them. Constantius arrived a few days later to receive the thanks of the populace, and a coin was struck commemorating his arrival, calling him ‘Redudctor Lucis Aeternae’ (‘restorer of Eternal Light’). The victory restored Britain to the Empire and shored up Constantius’ reputation, reputedly annoying Maximian who did not want him to get too popular and had bene hoping that after his initial five-year term as ‘Caesar’ (293-8) Diocletain’s promised review into his conduct would lead to the senior Emperor sacking him in Maxentius’ favour or moving him to the East. Instead, Constantius was the hero of the hour and even the obsessively prestige-conscious Diocletain did not mind that his subsequent march to the North of Britain and restoration of the raid-hit Antonine Wall (short of troops since Carausius moved half its garrison South in 293) led to him recommending its abandonment as too expensive.

A pict, as drawn in John Cassell's Illustrated History of England

Constantius had defeated the new local tribal coalition of the so-called ‘Picts’ (‘Painted People’ , so-called from their tattoes), an emergant grouping of Caledonian chieftaincies in the Highlands, and forced them into giving tribute and hostages – but he advised Maximian and through him Diocletain that it would be cheaper to cut all the garrisons North of Hadrian’s Wall and rely on bribed pro-Roman local nobles, who had had a century to be ‘Romanised’ , learn Latin, dress in Roman togas, and replace their wooden huts in hillforts by stone unfortified residences as ordered by the Empire, to keep order. These descendants of ancient tribal nobles were still loosely connected to traditional regional lordships of the Votadini (Lothian) and Selgovae (Clydesdale) tribes, but they had made a successful living out of raising horses for the army and cattle and sheep for Roman markets and now they continued as Roman allies beyond the new frontier, raising their own militias as Roman auxiliaries to keep the Picts at bay and the personal relationships that Constantius secured with their chiefs kept the peace North of Hadrian’s Wall reasonably well for a generation.

Constantius also kept up the ‘Classis Britanniae’ fleet, under carefully-watched admirals who were rotated in office regularly so none could turn their juniors into a personal clientele as Carausius had done, to deal with any more Frankish raids, and indeed as the thoroughly chastised Franks now settled down as farmers NE of the Rhine they were replaced as a pirate menace by the Saxons to their North who were further from the frontier. The South-Eastern British coast’s regional command thus became known after c.300 as the ‘Saxon Shore’, with the land-based troops there commanded by a new ‘Count’ – who could also be used to counter the fleet if the latter mutinied again. Extra forts were built at Anderida (Pevensey), Gariannonum (Burgh Castle near Great Yarmouth) and Brandonium (Brancaster) around 300 by Constantius, and when the forts were not being used for military and naval patrols they served to collect British corn and other food-supplies being exported to the Rhine to feed the enlarged Rhine army. Meanwhile Maximian brought extra troops from the upper Danube to reinforce the Rhine defences while some of the troops usually stationed there were in Britain with Constantius in 296 and kept them on thereafter, but the Germans (especially the Franks) did not take advantage of the ‘Caesar’s absence and the Rhine frontier was quiet for another decade.

In 297 the East was hit by the rebellion of local ‘duces’ (provincial military commanders) Achilleus and Domitius Domitianus in Egypt, based at Alexandria, which took advantage of the anger of local nobles and urban crowds alike at the higher taxes imposed on the wealthy city by the new over-governor/ ‘Augustal Praefect’ of all Egypt, Dionysius of Melitene. They were joined by the armies of the upper Nile frontier and a large grouping of refugee peasants who had fled to the city of Thebes from recent desert nomad raids on their farms and blamed the Emperor for not sending more troops to Egypt. Diocletian went there with an army to suppress them in person. The Persians under Bahram II’s younger brother Narses (a usurper who had murdered his nephew Bahram III son after his accession in 293 and faced plots by the latter’s allies ) took advantage to invade Mesopotamia, and Diocletian summoned his ‘Caesar’ Galerius from his command against the raising Carpi in Dacia to repel them. He himself was too busy besieging the rebels in well-walled and provisioned Alexandria, and the siege took six months to succeed as the rebels feared harsh punishment and refused tall inducements to surrender.

Eventually the Imperial troops got into the city via an aqueduct-tunnel and the angry Emperor had the sullen and unwelcoming populace massacred to teach them a lesson. He then constructed a large new military base in the ‘Brucheum’ district to hold the restless city and its huge population of nearly half a million people down, and made sure that no commanders or senior officers with local connections or sympathies served there to minimise the risk of rebellion. This kept Alexandria quiet and the Emperor deported a large part of the old Ptolemaic court nobility’s Greek descendants to his capital at Nicomedia to keep an eye on them – which had the incidental effect of a body of educated Greek intellectuals who had been taught at the local schools set up at the ‘Great Library’ research/ archive complex relocating to Nicomedia too and so coming to have an influence on the court, not least in their antagonism to Christianity. The more Aramaic/ Syrian / Palestinian Christian community in Alexandria, long at feud with the local Greeks since the Jewish vs Greek riots there in the C1st AD, had stayed aloof from the Greek-led revolt of Achilleus and were not deported by Diocletian, which was to give their community an advantage in obtaining recruits and influence at the Egyptian capital.

Detail of Galerius attacking Narseh on the Arch of Galerius. Photo taken by J. Matthew Harrington and shared under the CC BY 2.5 licence.

Galerius arrived in Syria to find the Persians already had overrun most of Roman Mesopotamia; he advanced quickly to cross the Euphrates at Callinicum with his smallish ‘comitatus’, reputedly ignoring Diocletian’s instructions to wait until he had reinforcements and could tackle their heavy cavalry on equal terms. Crucial Syrian and Arab cavalry had been called off to Egypt by Diocletain – as the well-informed Persians knew. Over-confident of his capabilities, Galerius was seriously defeated in a surprise Persian cavalry ambush near Callinicum and had to retire back across the river abandoning Rome’s remaining possessions East of it. Diocletian arrived at Antioch after finishing his post-rebellion ‘clean-up’ in Egypt to hear of the disaster, summoned Galerius from his headquarters, and according to one story made him walk for a mile in front of his chariot into Antioch in disgrace. But he was too cautious either to sack the ‘Caesar’ or to rush troops to protect the abandoned fortresses of Roman Mesopotamia and risk another defeat, this time to himself, and he coolly left them to be starved out or stormed – the sieges would after all cost Persia casualties – while he summoned more troops to Syria and built and trained a safely huge army through 297. He also started reforms of the tax-system to raise regular sums of money dependent on the fluctuating demands of the inflated State bureaucracy and army in place of the old fixed assessments. An annually revised budget was instituted and provinces were regularly re-graded for taxation levels according to their ability to pay; he was ruthless in insisting that even inner provinces far from the frontier had to pay up a full rate of taxes like the outer ones and he had the wealthy ‘diocese’ of Northern Italy subjected to taxation for the first time, ending its traditional exemption. Danubian troops and Sarmatian (Wallachian tribal) mercenaries were sent to Syria to strengthen the army there for the next Persian campaign.

In 298 Galerius was sent to invade Armenia in support of the fugitive king Tiridates who Narses had evicted in 297 after finishing overunning Roman Mesopotamia – Diocletian wanted to tackle the Persians well away from the open plains that suited their heavy cavalry - and Narses attacked him with a large Persian army. He took the Persians by surprise in a night-time attack on their camp in hilly country and they fled in disorder, Narses wounded and abandoning the royal harem. The Persians were left humiliated and Galerius and Diocletian could play up the victory as a repeat of Alexander’s over Darius III at Issus in 331 BC, where also the Persian royal harem had been captured. Narses was ridiculed as being as hopeless as Darius, and Galerius sent his prisoners, including Narses’ wives, to Diocletian before meeting him at Nisibis which they retook together; a separate Roman army meanwhile operated in the middle Euphrates valley to retake Dara and then Edessa. Galerius then invaded the Tigris valley with Narses unable to muster a force to stop him, and marched down-river to Ctesiphon.

The Persian capital was occupied by Rome again, and the Romans marched on to Charax (Basra) but the cautious Diocletian decided against the cost of annexing any territory. Narses sent an embassy to negotiate the return of his harem and ask about a treaty as rumours were spread that Galerius intended to dust off Aurelian’s plan to break up the Persian empire and had refugee cousins of Narses’ at his camp ready to help; the Persians are reputedly impressed that the Romans had not touched any of the royal women that they successfully offered peace. Diocletian was invited to send an embassy to Narses. Narses met the embassy on a raft in the middle of the Tigris downstream from occupied Ctesiphon, and due civilities were exchanged with the Emperor’s young protégé Constantine, Constantius' son, among the Roman courtiers present and keeping an eye on proceedings for his father. The peace-treaty agreed the return of the five provinces of Roman Mesopotamia, with additional lands (including Corduene/Cadousia) as far as the upper Tigris protecting the South-Eastern approaches to Armenia which returned to being a Roman protectorate. Iberia is confirmed as a Roman protectorate.

Tiridates was guaranteed his throne by Persia as well as Rome – and despite his coronation by Diocletian and new role as his ‘guard-dog’ on the NW Persian frontier was soon to dismay him by adopting Christianity from a travelling mission of Syrian enthusiasts, taking up the concept of how the religion could add to a monarchy’s prestige by getting its priests to preach loyalty to the secular power as ordained by God. (Rumour had it that Constantine also picked up this idea during his time in Syria and Mesopotamia in 298-9). The frontier was thus advanced further than it had been since the time of Trajan by the treaty signed in spring 299 at Nisibis, but Galerius was allegedly dismayed that he did not have the chance to annex further territory and use Aurelian’s plan to break up Persia.


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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