367–368 AD – Great Barbarian Conspiracy

What Happened

In AD 367, Roman Britain faced a catastrophic and unprecedented crisis known as the Barbarica Conspiratio (the Great Barbarian Conspiracy). According to the historian Ammianus Marcellinus, a coordinated and simultaneous assault was launched against the province by multiple enemies from different directions. The Picts from northern Scotland breached Hadrian's Wall; the Scotti (Scots) from Ireland attacked the western coasts; and the Franks and Saxons from the continent raided the eastern and southern shores.

The situation was exacerbated by widespread treachery within the Roman military establishment. The areani (or arcani), a network of frontier scouts and spies tasked with providing early warning of barbarian movements, had been bribed by the invaders to conceal their approach. Furthermore, many of the auxiliary troops manning Hadrian's Wall either deserted or actively joined the attackers.

The resulting chaos was devastating. The Comes Litoris Saxonici (Count of the Saxon Shore), Nectaridus, was killed in battle, and the Dux Britanniarum (Duke of the Britains), Fullofaudes, was either killed or captured. The Roman defensive system collapsed entirely. Bands of barbarians roamed freely across the province, looting villas, burning settlements, and enslaving the population. The provincial capital, Londinium (London), was effectively besieged by marauding warbands.

The crisis was so severe that Emperor Valentinian I, campaigning on the Rhine, was forced to dispatch his most capable general, Count Theodosius (father of the future Emperor Theodosius I), to restore order. Theodosius arrived in Britain in AD 368 with a large force of elite field army troops (comitatenses). He landed at Richborough and marched on Londinium, systematically hunting down the scattered barbarian bands, recovering stolen loot, and freeing captives. He then spent the next year reorganizing the province's defences, rebuilding forts, disbanding the treacherous areani, and offering amnesties to deserters who returned to their units.

Why It Mattered

The Great Barbarian Conspiracy of AD 367–368 was a profound shock to the Roman system in Britain. It demonstrated the extreme vulnerability of the province to coordinated attacks and the fragility of its frontier defences when undermined by internal corruption and treason. The loss of the two senior military commanders and the collapse of Hadrian's Wall highlighted the failure of the existing security arrangements.

Theodosius's successful restoration of order, while impressive, marked a significant shift in the nature of Roman rule in Britain. The province was increasingly militarized, with a greater reliance on mobile field armies rather than static frontier garrisons. The rebuilding of the forts, particularly along the Saxon Shore, reflected a defensive posture focused on repelling seaborne raids rather than projecting power into the north. The crisis also accelerated the decline of the villa economy in some areas, as wealthy landowners sought the safety of walled towns or abandoned their estates entirely. The events of 367–368 foreshadowed the eventual collapse of Roman authority in Britain half a century later.

Human Perspective

For the Romano-British population, the Great Barbarian Conspiracy was a period of unimaginable terror and devastation. The sudden collapse of the military defences left them entirely exposed to the violence and rapacity of the invading warbands. The looting of their homes, the destruction of their livelihoods, and the enslavement of their families must have been a profound and enduring trauma. The sight of Londinium besieged by barbarians underscored the complete failure of the Roman state to protect its citizens.

For the Roman soldiers, the crisis was a humiliating disaster. The treachery of the areani and the desertion of their comrades shattered the cohesion and discipline of the army. The deaths of their commanders, Nectaridus and Fullofaudes, left them leaderless and demoralized. The arrival of Count Theodosius and his elite troops brought salvation, but the subsequent reorganization of the defences and the disbanding of the scouts highlighted the deep mistrust that now permeated the military establishment. The events of 367–368 demonstrated that the security of Roman Britain could no longer be taken for granted, and that the province was increasingly reliant on massive interventions from the continent to survive.