Drought left Britain too hot to handle for the Romans
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.
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.
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.'
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All that heavy stuff should sink, via gravity, into the core. But apparently it hasn't. If the core is so light, then what could it possibly be made of? Scientists are scrambling for answers. This fuzzy core doesn't fit with anyone's model for planetary formation. Some scientists have suggested a giant meteor crashed into a once solid core, smashing it up and forcefully mixing it with the metallic hydrogen ocean. Levin wonders whether we simply don't understand the physics yet. 'We're talking about temperatures and pressures much higher than anything we're used to,' he says—conditions so severe that it's difficult to create them in laboratories. Other blockbuster findings from Juno concern Jupiter's moons. The probe's reconnaissance of two icy orbs—the pockmarked Ganymede and the ocean-concealing Europa (the target of a recently launched NASA habitability mission)—created breathtaking portraits of these dynamic worlds while also revealing some unusual chemistries. 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Many thought that this mechanism, known as tidal heating, was so powerful that it created a continuous ocean of magma under the surface rather than the smaller, individual magma reservoirs that fuel Earth's volcanoes. The Galileo mission seemed to back that idea up: it detected an electrically conductive layer under Io's crust suggestive of a magma sea. But when Juno flew perilously close to Io on two occasions, getting within 900 miles of the violent surface, it found no trace of a shallow magma ocean. Mura now suspects Io's magma is partitioned into a maze of rocky tunnels, occasionally bubbling up into open rocky maws wherever the tunnels reach the surface. Nobody knows for sure; in typical Juno style, the observations have raised more questions than answers. But at least while scientists ponder possible solutions, they can marvel at Io's unbound ferocity. 'We discovered the largest eruption ever recorded,' Bolton says. In December 2024 Juno's infrared instrument detected a heat spike in the moon's southern hemisphere that briefly blinded the spacecraft's JIRAM instrument: a paroxysmal outpouring of lava spread over 40,000 square miles, enough to cover a quarter of California. It's producing more energy than the total annual energy output of humanity. 'And we still see it going on,' Bolton adds. By all accounts, Juno should be dead by now. The radiation should have already broken it or at least one of its instruments. Somehow it lasted well beyond its prime mission timeline, which ended in 2021. If an additional three-year extension is approved, Juno could get a better look at the planet's ghostly ring system, and some of its lesser-known innermost moons. But there's no telling how long the aging spacecraft could survive. 'It could grow old, and something could fail,' Bolton says. Perhaps 'the radiation will kill something so important that we can't function anymore.' Whenever the vehicle's end comes, it will go out in flames, spiraling toward the gas giant it spent its entire life interrogating. 'Eventually Juno will crash into Jupiter on its own,' Bolton says. But the spacecraft's legacy is already clear. Juno revealed Jupiter to be a far more confounding place than anyone dared imagine, forcing scientists to throw out reams of outdated ideas about planetary formation. It's also revealed how future spaceflight missions can defend themselves from the worst radiation in the solar system. The Juno team, having emulated its namesake's god-defying powers, is openly proud, Becker says. 'What an amazing success story for NASA.' Solve the daily Crossword
