Prelude to the Barbarian Conspiracy

By the year 350, Emperor Constans had passed away, and Magnentius, who had both British and Frankish ancestry, had seized control in the Western Provinces. Meanwhile, Constantius II held dominion over the Eastern regions. In Britain, Flavius Martinus served as the Vicarius, essentially the governor responsible for the administrative organization of the provinces. He enjoyed a favorable reputation among the British aristocracy, who regarded him as both equitable and straightforward in his interactions with them. Ammianus, a contemporary Roman historian, describes Martinus by saying:

Martinus, who at that time governed these provinces as deputy, being greatly concerned for the sufferings inflicted on innocent men, and making frequent entreaties that those who were free from all guilt might be spared, when he found that he could not prevail, threatened to withdraw from the province, in the hope that this malevolent inquisitor, Paulus, might be afraid of his doing so, and so give over exposing to open danger men who had combined only in a wish for tranquillity.

The Roman History, Book XIV (353-356AD)

This indicates that Martinus, despite being well-liked, lacked significant authority. He was essentially acting as a stand-in for the Praetorian Prefect, which greatly limited his power following the suppression of Magnentius’s revolt.

Magnentius, often labeled a barbarian by contemporary authors, was born in Samarobriva (present-day Amiens, northeastern France) to a British father and a Frankish mother. He was known for his tolerance towards both paganism and Christianity. Climbing the ranks of the Roman military, he eventually led the emperor’s personal legions, the Loviani and Herculiani seniores. His ascent to power occurred in Autun, where, following the Roman army’s dissatisfaction with Constans’s actions, he had Constans executed after his escape, near the Pyrenees by someone named Gaiso (Consul in 351).

It is believed that Magnentius visited Britain around February 350 AD, likely to gather funds for his impending war efforts and to draft some of the local legions. He depleted Britain of its movable forces and drained the frontier garrisons of Gaul to bolster his own ranks. For Magnentius, this marked the start of his quest for complete control over the Roman empire. He unified the forces of Britain and Gaul, garnering support from his Germanic kin, the Franks and Saxons, as well as the Spaniards, and marched towards Trier and then Rome, which eventually fell to him. Magnentius sought acknowledgment from Constantius as the legitimate ruler of the Western Empire, but Constantius, given the Flavian dynasty’s 50-year reign since Constantine I, declined.

In retaliation, Constantius II encouraged Germanic tribes to cross into Gaul over the Rhine, a move intended to delay Magnentius but which also had lasting consequences. Despite this, Magnentius, with the help of his Frankish allies, managed some degree of control over the invaders sanctioned by Constantius. Constantius, on his part, continued to enlist more Germanic forces. Magnentius recruited the Keltoi and Galatai, but, as stated by Emperor Julian, his most fervent supporters were:

The most enthusiastic of his followers were, in virtue of their ties of kinship, the Franks and Saxons, the most warlike of the tribes who live beyond the Rhine and on the shores of the western sea.

Julian, Oration I: Panegyric in Honour of Constantius

In 351 AD, a colossal confrontation occurred at the Battle of Mursa Major, now within the borders of modern Croatia. This clash led to a staggering loss of 52,000 soldiers, significantly weakening the Roman military forces. It would be some time before Constantine could mount another offensive. However, by 353, he had successfully defeated Magnentius at Mons Seleucus in the southern regions of France.

Magnentius’ command in Britain, led by Gerontius (also known as Keraint or Gereint), underscores the deep connections Magnentius had with the British provinces and their military support that likely assisted his rise to power in 350. The possibility that Gerontius might be the same individual as Keraint ap Genedos from Welsh genealogies raises intriguing questions. It’s speculated that “Genedos” might be a distorted Welsh version of Magnentius’ name. Welsh legends tell of Gerontius elevating his kin to prominent positions in Britain: Tegid (Tacitus) was placed in charge of the far north, producing a lineage that included Cunedda. Another brother, Eudaff, was granted control over Wales, and it’s suggested he might have been the same Eudosius who served as Praetorian Prefect for Magnus Maximus. Gerontius’ first son, Cynan, received Dumnonia and later Armorica, eventually rising to the role of Magister Militum, likely overseeing Armorica. The matrimonial alliances within this narrative, such as Keraint’s daughter marrying Magnentius and Eudaff’s daughter marrying Magnus Maximus, though fascinating, remain historically unverified. The only substantial link is Gerontius’ role as Comes Britanarium in 350.

With Britain’s military forces diminished, the northern Barbarian tribes and the Scoti from Ireland likely recognized the weakened state but did not launch significant offensives during Magnentius’ reign. Magnentius’ visit to Britain in 350 might have involved negotiations that deterred attacks. Julian, later Caesar of Gaul and Britain, references a broken treaty with the Scots and Picts around 359/60, suggesting earlier agreements.

Following Magnentius’ demise in 353, his general Gerontius faced torture and exile, though his destination remains a mystery. Despite these tribulations, Britain remained affluent and prosperous, yet was on the brink of experiencing Emperor Constantius’ fury.

The year 353 marked the beginning of threats from more aggressive entities, including the Huns moving westward, prompting a ripple effect that drove Germanic tribes into Roman territories in panic.

By 354, Britain faced a pivotal moment. The Roman aristocracy in Britain was decimated, its honourable but fragile Governor Martinus died by suicide, and the year concluded with a rebellion under Carausius II.

Of this court a most conspicuous member was Paulus, the secretary, a native of Spain, a man keeping his objects hidden beneath a smooth countenance, and acute beyond all men in smelling out secret ways to bring others into danger. He, having been sent into Britain to arrest some military officers who had dared to favour the conspiracy of Magnentius, as they could not resist, licentiously exceeded his commands, and like a flood poured with sudden violence upon the fortunes of a great number of people, making his path through manifold slaughter and destruction, loading the bodies of free-born men with chains, and crushing some with fetters, while patching up all kinds of accusations far removed from the truth. And to this man is owing one especial atrocity which has branded the time of Constantius with indelible infamy.

The Roman History, Book XIV (353-356AD)

These events severely undermined the nation’s internal stability, enabling the Picts and Scoti to resume raids. The disturbances were significant enough to necessitate intervention by Roman legions from afar. This tumultuous period can be attributed to Paulus Catenus, sent by Constantius to target Magnentius’ supporters. Upon discovering the vulnerable Governor Martinus in 354, Paulus exceeded his authority, implicating a vast number of the British Roman elite in treason, earning him the nickname Catenus – “The Chain.” The historian Ammianus Marcellinus provides a detailed account of these harrowing events.

The narrative around Martinus illustrates his incapacity to effectively counteract Paulus Catena, highlighting a broader theme of weakened leadership facing ruthless exploitation. Paulus Catena’s eventual fate, being executed by fire around 362 for his transgressions, marks a grim but fitting end to his tyranny.

Britain, during this period, was left in a precarious situation. With the Roman elite decimated or imprisoned and the harsh enforcers of Catena’s will in control, conditions were ripe for revolt. The emergence of Carausius II as a leader signals a critical juncture; driven by desperation, those remaining rallied around a figure who symbolized resistance against Rome’s oppressive actions. The decision to adopt the name of a previous usurper suggests an attempt to invoke a legacy of defiance.

By 354, Carausius II faced the daunting challenge of defending a province stripped of its military might by Magnentius and further weakened by the purges and expulsion of leaders by Paulus Catena. His leadership through these trials into the following year underscored the dire state of Britain’s defenses, a vulnerability surely noted by neighboring threats.

The appointment of Julian as Caesar of Britain and Gaul in 355 by Constantius highlights the empire’s stretched resources and priorities, with Julian’s attention largely occupied by threats in Gaul. This left Britain marginally defended and increasingly exposed to raids from various barbarian groups, exacerbating the instability and leading to a reliance on Rome for assistance once more.

Carausius II’s reign, evidenced by coinage issued under his name, reflects an era marked by turmoil and strategic dilemmas. The inscriptions on these coins hint at a complex relationship with the broader Roman Empire, perhaps indicating a recognition of imperial authority or an aspiration towards legitimacy.

Julian’s campaigns against the Alamanni and the subsequent grain shortages in Rome reveal the interconnected challenges facing the empire, where military engagements directly impacted the urban populace’s wellbeing.

By 358-359, the situation in Britain had deteriorated further with significant invasions by the Scots and Picts. The cessation of Carausius II’s coinage suggests his downfall and the resultant vulnerability of Britain to raids, painting a picture of a once robust province now grappling with fragmentation and external pressures.

The discovery of a possible tomb for Carausius II in Penmachno, Gwynedd, Wales, marked by a cairn stone, adds a tangible element to the historical narrative, potentially offering insights into the final chapter of a figure who stood at the heart of Britain’s tumultuous late Roman period.


The inscription ‘Carausius lies here in this cairn’ serves as a poignant testament to the final resting place of Carausius II, situating his death within the broader context of conflict against the Picts. The dating of the cairn to between the 4th and late 5th century aligns with historical accounts of Carausius II’s struggle and eventual demise, reinforcing the likelihood that this site marks the burial of the usurper who sought to defend Britain against its adversaries.

At the same time, the expansion of the Desi in Wales, led by Aed Brosc from County Waterford, reflects the broader migratory and settlement patterns shaping the British Isles during this tumultuous period. These movements, indicative of the fluid and often volatile nature of territorial control and cultural integration, played a significant role in the evolving landscape of post-Roman Britain.

The severe raids by the Picts and Scots in 359 overwhelmed Britain’s defenses, prompting a desperate plea for assistance from the Roman Empire. Julian’s response, dispatching legions under Lupicinus in 360 AD, marked a significant Roman intervention aimed at stabilizing the region. The inclusion of troops from diverse backgrounds such as the Herulians, Batavians, and Moesians underscores the empire’s commitment to reinforcing its beleaguered province.

Ammianus Marcellinus, offers insights into this critical intervention, chronicling the efforts to restore order and security to Britain. The narrative surrounding Lupicinus and his forces captures a moment of concerted military response to the external threats faced by Britain, highlighting the complexity of the empire’s relationship with its provinces during a time of widespread challenges.

These were the events which took place in Illyricum and in the East. But the next year, that of Constantius’s tenth and Julian’s third consulship, the affairs of Britain became troubled, in consequence of the incursions of the savage nations of Picts and Scots, who breaking the peace to which they had agreed, were plundering the districts on their borders, and keeping in constant alarm the provinces exhausted by former disasters, Cæsar, who was wintering at Paris, having his mind divided by various cares, feared to go to the aid of his subjects across the channel (as we have related Constans to have done), lest he should leave the Gauls without a governor, while the Allemanni were still full of fierce and warlike inclinations.

Therefore, to tranquillize these districts by reason or by force, it was decided to send Lupicinus, who was at that time commander of the forces; a man of talent in war, and especially skilful in all that related to camps, but very haughty, and smelling, as one may say, of the tragic buskin, while parts of his conduct made it a question which predominated—his avarice or his cruelty.

The Roman History, Book XX (360AD)

This episode, situated within the broader sweep of late Roman military and political dynamics, illustrates the intricate web of interactions between Rome and its territories. It underscores the persistent threats from beyond the empire’s borders and the measures taken to address these challenges, reflecting both the resilience and vulnerabilities of Roman authority in the face of external pressures.

In 360, Lupicinus landed in Britain with his legions and swiftly addressed the raids by the Picts and Scots. He appointed Alypius as Vicarius, Fullofaudes as Comes Britanarium, and Nectarides as Comes Maritimi Tractus (General of the Coastal Regions), marking the beginning of a strategic response to the threats facing Britain. The attacks had precipitated the decline of the villa society in Britain, leading to widespread abandonment of villas, and signs of neglect in towns and villages by the century’s end.

Alypius, serving as the Vicarius of Britain, was tasked with the restoration and maintenance of crucial infrastructure, including Hadrian’s Wall and the coastal forts in Kent and East Anglia, likely operating from London. His tenure was short-lived, however, as he was soon recalled to oversee the reconstruction of the Temple of Jerusalem.

Fullofaudes, assuming the role of Comes Britanarium, brought his Germanic heritage, possibly Vandal or Goth, to his position, likely making York his base. Nectarides, tasked with safeguarding the southern and eastern shores, brought a Greek or Roman background to his duties, possibly operating from the Saxon Shore in Kent or East Anglia.

From 360 to 366, Britain focused on fortifying its defences, enjoying five years of relative tranquillity until the Scots and Picts, possibly joined by other Germanic groups, launched a more organized assault in 366/7, challenging Britain’s security once again.