A new study from the University of Cambridge has uncovered strong evidence that extreme drought played a key role in one of Roman Britain’s most chaotic and devastating events: the “Barbarian Conspiracy” of 367 CE.
This was a moment when Roman control over Britain was severely shaken by coordinated invasions from the north, west, and south.
Using tree-ring records from ancient oak trees, scientists reconstructed past climate conditions and found that southern Britain experienced three years of severe summer drought from 364 to 366 CE.
This rare and prolonged dry spell likely caused widespread crop failures, food shortages, and deep societal strain—creating the perfect storm for rebellion and invasion.
The Barbarian Conspiracy saw Picts attacking from the north after Roman troops reportedly rebelled and abandoned their posts along Hadrian’s Wall.
At the same time, the Scotti from Ireland struck from the west, and Saxon raiders landed in the south. Roman commanders were killed or captured, some troops deserted, and for a time, Roman Britain descended into near-total anarchy.
It took two years for Emperor Valentinian I to restore control, but many historians argue the province never fully recovered, and by around 410 CE, Roman rule in Britain came to an end.
The team, led by Ph.D. student Charles Norman, linked the droughts directly to this moment of collapse.
Tree-ring data showed that rainfall during the crucial April to July growing season dropped far below normal, with only 28–37 mm of rain falling compared to the long-term average of 51 mm.
This kind of rainfall deficit, they argue, would have devastated crops like spelt wheat and barley, which were heavily relied on for feeding the population and the Roman army.
Roman chroniclers from the time described widespread famine and desperation. The lack of grain likely caused major issues along Hadrian’s Wall and may have driven soldiers to rebel or abandon their duties. The researchers believe the food crisis weakened the Roman military presence and opened the door for invading groups to strike.
Interestingly, the drought conditions seem to have been limited to southern Britain. Other parts of Roman Europe didn’t experience the same level of climate stress, challenging older ideas that invaders were driven by their own famines.
The study also found that drought and conflict often went hand-in-hand across the Roman Empire. By analyzing 106 battles between 350 and 476 CE, the researchers discovered that many occurred shortly after dry years, suggesting that extreme weather often played a role in triggering unrest.
This research shows that even centuries ago, climate and conflict were closely connected. As the modern world faces more extreme weather events, the study highlights how environmental stress can still lead to serious social and political consequences.
