Drought left Britain too hot to handle for the Romans

Telegraph

17-04-2025

Roman rule in Britain was scuppered by three years of drought that led to rebellion and invasion, new tree-ring data suggests.
In 367 AD, tribes including the Picts, Scotti and Saxons banded together in a co-ordinated attack on Roman Britain which has been dubbed the Barbarian Conspiracy.
Now researchers believe that the invaders took advantage of famine and societal breakdown, caused by an extreme period of drought, to inflict crushing blows on weakened Roman defences.
The University of Cambridge used oak tree-ring records to reconstruct temperature and precipitation levels in Britain during the Barbarian Conspiracy and found evidence of severe summer droughts in 364, 365 and 366 AD.
Charles Norman, a doctoral student from Cambridge's Department of Geography, said: '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.'
The Barbarian Conspiracy was one of the most severe threats to Rome's hold on Britain since the revolt led by Boudica three centuries earlier.
Part of the garrison on Hadrian's Wall rebelled and allowed the Picts to attack the Roman province by land and sea.
Simultaneously, the Scotti invaded western Britain from modern-day Ireland and Saxons, from the continent, landed in the south.
During the unrest, senior Roman commanders were captured or killed, and some soldiers reportedly deserted and joined the invaders.
It took two years for generals dispatched by Valentinian I, Emperor of the Western Roman Empire, to restore order, but some historians argue that the province never fully recovered. Roman rule collapsed some 40 years later around 410AD.
Britain was in the 'utmost conditions of famine'
The new research shows that Britain experienced an exceptional sequence of remarkably dry summers from 364 to 366 AD where rainfall nearly halved.
Roman Britain's main produce were crops, such as spelt wheat and six-row barley, which were vulnerable to early summer droughts.
Accounts written at the time corroborate these drought-driven grain deficits.
By 367 AD, Ammianus Marcellinus, a Roman chronicler, described the population of Britain as in the 'utmost conditions of famine'.
Prof Ulf Büntgen, from Cambridge's Department of Geography, said: '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.'
Roman soldiers were partly paid in grain so a shortage is likely to have contributed to desertions in this period and a weakening of the army in Britain.
The experts believe the reduced grain supply to Hadrian's Wall provides a plausible motive for the rebellion there which allowed the Picts into northern Britain.
The researchers argue that military and societal breakdown in Roman Britain provided an ideal opportunity for peripheral tribes to invade the province en masse with the intention of raiding rather than conquest.
Link between climate and conflict
The researchers also expanded their climate-conflict analysis to the entire Roman Empire for the period 350 to 476 AD.
They reconstructed the climate conditions immediately before and after 106 battles, finding that a statistically significant number of battles were fought following dry years.
Tatiana Bebchuk, also from Cambridge's Department of Geography, said: '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.'