Ancient tree rings reveal a severe drought that weakened Roman Britain before the catastrophic “barbarian plot” in AD 367, when coordinated attacks from PICTS, Scots and Saxony destroyed the province.
Research led by the University of Cambridge, published in climate change, combines tree ring records with Roman historical records to demonstrate how climate extremes triggered a series of social collapses that ultimately led to Rome’s withdrawal from the UK.
“We don’t have much archaeological evidence for the ‘barbarian conspiracy’. The written narrative since then provides some context, but our findings provide explanations for the catalyst for this major event.”
By analyzing the ancient oak rings, the researchers reconstructed precipitation in southern England at a critical period. They found that during the critical April-July growing season, 364-366 CE rainfall was only 54-72% of normal levels – the severity of three consecutive droughts never continued in modern times.
“Three consecutive droughts will have a devastating impact on productivity in the most important agricultural areas of Rome, Britain. As Roman writers tell us, this brings food shortages, which brings all the devastating social impacts,” explained Professor Ulf Büntgen, co-author of the University Department of Cambridge.
For Roman Britain, the timing proved disastrous. Agricultural customs in the province relies on spring estate crops that are particularly susceptible to early summer droughts. As the harvest failed for three consecutive years, the supply of grain from the military garrison decreased. Roman chronicler Ammianus Marcellinus described the population of Britain as the “maximum famine condition” in AD 367.
This environmental crisis created the ideal conditions for the subsequent coordinated attack. The elements of the Roman garrison on Hadrian’s walls could be plagued by food shortages, rebelling and allowing northern tribes to pour into the province. Military leaders in the province were killed or captured, and some soldiers reportedly joined the invaders in desolate land.
The study also extended Britain to analyze climate patterns before 106 battles across the Roman Empire. They found a statistically significant battle pattern occurred during the drought period of Western empires.
“The relationship between climate and conflict is becoming increasingly clear, so these findings are not only important to historians,” said Tatiana Bebchuk, co-author of the University of Cambridge. “Extreme climate conditions lead to hunger, which can lead to social challenges and ultimately lead to complete conflict.”
Rome eventually restored order in Britain, but the province never fully recovered. Just 43 years after the savage plot, the last time the Roman government left Britain around 410 AD.
These findings suggest that even powerful empires may be vulnerable to environmental shocks cascading through agricultural systems and social structures, ultimately triggering conflict and political shifts.
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