A recent study spearheaded by the University of Cambridge has revealed that a sequence of severe droughts significantly contributed to the 'Barbarian Conspiracy' in late Roman Britain—a pivotal historical event that occurred in 367 CE. This research, published in Climatic Change, suggests that three consecutive dry years exacerbated societal and agricultural problems, leaving Roman defenses vulnerable to attacks from the Picts, Scotti, and Saxons.
The study utilized oak tree-ring data to reconstruct the climate in southern Britain, focusing on the years preceding and following the events of 367 CE. The findings indicated notably dry summers in 364, 365, and 366 CE, with average rainfall considerably below historical norms. "We don’t have much archaeological evidence for the ‘Barbarian Conspiracy'," said Charles Norman from Cambridge’s Department of Geography. "Written accounts from the period give some background, but our findings provide an explanation for the catalyst of this major event."
During this critical period, the Roman province of Britain's main agricultural outputs suffered immensely due to the drought. According to Professor Ulf Büntgen, "Three consecutive droughts would have had a devastating impact on the productivity of Roman Britain’s most important agricultural region." This shortage in food supply and the resulting societal destabilization created a fertile ground for military uprisings and external invasions.
The most severe drought conditions were confined mainly to southern Britain, an area dependent on spring and early summer rainfall, leaving its agricultural systems particularly vulnerable. As reported by the Roman historian Ammianus Marcellinus, by 367 CE, the population suffered "utmost conditions of famine."
The research team extended their analysis to cover the entire Roman Empire from 350 to 476 CE, finding a statistical correlation between climate conditions and conflict, with many battles occurring in the wake of dry years. Tatiana Bebchuk emphasized the ongoing relevance of this correlation, stating, "The relationship between climate and conflict is becoming increasingly clear in our own time so these findings aren’t just important for historians."
Led by Norman, Büntgen, Paul Krusic, and Tatiana Bebchuk from Cambridge, with Lothar Schwinden and Andreas Rzepecki from the Generaldirektion Kulturelles Erbe Rheinland-Pfalz, the study's multidisciplinary approach unites historical accounts with modern scientific techniques to illustrate the climate's impact on Roman Britain.
The occurrence of these droughts during a time when Britain was already weakened by military resource depletion and other challenges underscores the vulnerability of the province, facilitating the coordinated influx of external tribes. Andreas Rzepecki noted, “Our findings align with the accounts of Roman chroniclers and the seemingly coordinated nature of the ‘Conspiracy’ suggests an organized movement of strong onto weak."
The understanding of climate's influence on historical events offers a lens through which current and future societal challenges may also be examined.