Jan Bartek – AncientPages.com – The “Barbarian Conspiracy” of 367 CE posed a significant threat to Rome’s control over Britain, comparable to the Boudiccan revolt three centuries prior. Historical records reveal that parts of the garrison on Hadrian’s Wall turned against Rome, allowing the Picts to launch attacks both by land and sea.
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Together, the Scotti from present-day Ireland invaded from the west, while Saxons from continental Europe landed in the south. This coordinated assault resulted in the capture or killing of senior Roman commanders, and some soldiers defecting to join the invaders. Throughout spring and summer, small raiding parties looted across the countryside, plunging Britain into chaos—a situation disastrous for Rome that took two years for generals sent by Valentinian I, Emperor of the Western Roman Empire, to rectify. The official Roman presence in Britain came to an end around 410 CE.
Was there a specific event that triggered the Barbarian Conspiracy?
A study by scientists at Cambridge University suggests a significant environmental factor behind this upheaval: three consecutive years of drought may have contributed significantly to these events. By analyzing oak tree-ring data to reconstruct climate conditions in southern Britain during this period and correlating it with existing Roman accounts, researchers propose that severe summer droughts in 364, 365, and 366 CE played a crucial role in triggering these pivotal historical developments.
“We don’t have much archaeological evidence for the ‘Barbarian Conspiracy’. Written accounts from the period give some background, but our findings provide an explanation for the catalyst of this major event,” First author Charles Norman, from Cambridge’s Department of Geography, said in a press release.
Researchers have discovered that southern Britain experienced an extraordinary series of dry summers from 364 to 366 CE. During the period from 350 to 500 CE, the average monthly reconstructed rainfall during the main growing season (April–July) was typically around 51 mm. However, in 364 CE, this figure dropped significantly to just 29 mm. The situation worsened in 365 CE with only 28 mm of rainfall, and although it slightly improved to 37 mm in the following year, the region remained in crisis.
Between 1836 and 2024 CE, southern Britain experienced droughts of similar severity only seven times—primarily in recent decades—and none were consecutive. This highlights how unusual these Roman-era droughts were. No other significant droughts were identified in southern Britain during this timeframe (350–500 CE), and other parts of northwestern Europe did not experience these conditions.
In Roman Britain, key agricultural products included crops such as spelt wheat and six-row barley. Due to its wet climate, spring sowing was more feasible than winter planting; however, this made crops susceptible to moisture shortages during late spring and early summer. Consequently, early summer droughts could result in complete crop failures.
The researchers also reference accounts by Roman chroniclers that support evidence of grain shortages caused by these droughts. By 367 CE, Ammianus Marcellinus described Britain’s population as suffering under “utmost conditions of famine.”
“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 destabilizing societal effects this bring,” Professor Ulf Büntgen, from Cambridge’s Department of Geography said.
“Drought from 364 to 366 CE would have impacted spring-sown crop growth substantially, triggering poor harvests,” Charles Norman said. “This 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.”
The study suggests that grain played a crucial role in the relationship between soldiers and the army, and shortages may have led to increased desertions during this period, contributing to the general weakening of the Roman army in Britain.
Additionally, Roman Britain’s geographic isolation, coupled with the severity of a prolonged drought, likely hindered Rome’s ability to address these deficits. Researchers ultimately suggest that the military and societal breakdowns in Roman Britain created an ideal opportunity for peripheral tribes, such as the Picts, Scotti, and Saxons, to invade en masse with raiding intentions rather than conquest.
Hadrian’s Wall. Credit: Adam Cuerden – Public Domain
Their findings show that severe conditions were mainly confined to southern Britain, challenging the notion that famines elsewhere prompted these tribes to invade.
“Our findings align with the accounts of Roman chroniclers and the seemingly coordinated nature of the ‘Conspiracy’ suggests an organised movement of strong onto weak, rather than a more chaotic assault had the invaders been in a state of desperation.
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, while immigratory pressures increased.
These factors limited resilience, and meant a drought induced, partial-military rebellion and subsequent external invasion were able to overwhelm the weakened defences,”
Researchers extended their climate-conflict analysis to encompass the entire Roman Empire during the period from 350 to 476 CE. By reconstructing climate conditions immediately before and after 106 battles, they discovered that a statistically significant number of these conflicts occurred following dry years. This finding suggests a potential link between climatic conditions and historical conflict patterns within this era.
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“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,” Tatiana Bebchuk, from Cambridge’s Department of Geography said.
The study was published in the journal Climatic Change
Written by Jan Bartek – AncientPages.com Staff Writer
