New research has revealed that a succession of exceptionally dry summers, leading to famine and social upheaval, played a crucial role in one of the most serious challenges to Roman authority in Britain. This period of environmental hardship set the stage for what is historically referred to as the “barbarian conspiracy,” in which various tribal groups including the Picts, Scotti, and Saxons exploited the empire’s vulnerability to launch devastating attacks on Roman territories.
The rebellion unfolded during the spring and summer of AD367, a time when Roman defences were severely compromised. Senior commanders were either captured or killed, and reports suggest that some Roman soldiers abandoned their posts to join the invaders. The ensuing chaos required a concerted military response, with generals sent by Emperor Valentinian I of the Western Roman Empire taking two years to re-establish control. Despite these efforts, the final vestiges of formal Roman administration in Britain disappeared approximately four decades later.
The findings, published in the journal Climatic Change, stem from an interdisciplinary study conducted by researchers affiliated with the University of Cambridge’s department of geography. By analysing oak tree-ring data, the team reconstructed patterns of temperature and rainfall in southern Britain during the mid-fourth century. Their analysis revealed a dramatic decline in summer rainfall over three consecutive years: from an average monthly growing season rainfall of 51mm between AD350 and 500, levels dropped to 29mm in AD364, 28mm in AD365, and remained below average at 37mm in AD366.
Professor Ulf Büntgen explained the agricultural consequences of these conditions, stating, “Three consecutive droughts would have had a devastating impact on the productivity of Roman Britain’s most important agricultural region. As Roman writers tell us, this resulted in food shortages with all of the destabilising societal effects this brings.”
The study also drew upon Roman historical accounts, noting that by AD367, Britain was enduring "the utmost conditions of famine,” as described by the soldier and historian Ammianus Marcellinus. The resulting grain shortages are believed to have contributed to weakened support structures, particularly in vital military outposts such as Hadrian’s Wall. Charles Norman of Cambridge’s geography department emphasised this connection: “The poor harvests would have reduced the grain supply to Hadrian’s Wall, providing a plausible motive for the rebellion there which allowed the Picts into northern Britain.”
This period of drought-related famine likely contributed to a broader decline in military cohesion, as food scarcity and hardship may have encouraged desertion and diminished the overall strength of Roman forces on the island. The combined effect of internal instability and environmental stress created an opening for peripheral tribal groups to invade and wreak havoc.
Commenting on the wider implications of this study, Tatiana Bebchuk, also of Cambridge’s department of geography, highlighted the contemporary relevance of the findings: “The relationship between climate and conflict is becoming increasingly clear in our own time, so these findings aren’t just important for historians. Extreme climate conditions lead to hunger, which can lead to societal challenges, which eventually lead to outright conflict.”
The research further identified that southern Britain endured no other comparable droughts during the AD350–500 period, and that neighbouring regions in north-west Europe largely escaped similar dry spells. Andreas Rzepecki, from the Rhineland-Palatinate General Directorate for Cultural Heritage, noted the broader strategic context, observing, “The prolonged and extreme drought seems to have occurred during a particularly poor period for Roman Britain, in which food and military resources were being stripped for the Rhine frontier. These factors limited resilience, and meant a drought-induced, partial-military rebellion and subsequent external invasion were able to overwhelm the weakened defences.”
Expanding their investigation beyond Britain, the researchers examined climate data surrounding more than 100 battles across the Roman Empire between AD350 and 476. Their analysis found a statistically significant correlation between dry years and the occurrence of battles, suggesting that episodes of drought and subsequent resource scarcity may have been a widespread catalyst for conflict during the empire’s later stages.
Together, these insights offer a nuanced understanding of how environmental factors intersected with political and military vulnerabilities in late Roman Britain. The convergence of climatic hardship and socio-political pressures during the barbarian conspiracy thus emerges as a key dynamic in the decline of Roman influence on the island.
Source: Noah Wire Services