Molly Glick writes:

Roman Britain collapsed into chaos in the spring of 367 A.D.—the rival Picts attacked by land and sea, while the Scotti barged in from the west and Saxons from the south. Anarchy ensued in an event that’s now known as the Barbarian Conspiracy: The invaders captured and murdered senior commanders, and some Roman soldiers may have even joined in. It’s considered a pivotal event in the abandonment of Roman Britain.

Historians have surmised some of the potential causes behind this rebellion, like the Western Roman Empire’s fading control of the region and its growing financial troubles. But these circumstances don’t fully explain the abruptness with which Roman Britain fell to its foes, and the scarce written records from the time don’t offer solid explanations. For clearer answers, researchers are asking the trees.

“The Barbarian Conspiracy is an iconic event with a clear date, where we knew what happened—but not why,” says Ulf Büntgen, a geographer and ecologist at Cambridge University.

Büntgen and his colleagues decided to consult tree ring data, from oaks both living and dead, and found the record suggests that three summers of brutal drought preceded the Barbarian Conspiracy. Dry years yield thinner tree rings than wet ones. To reconstruct important details of the Barbarian Conspiracy, the authors consulted records written by Greek and Roman soldier and historian Ammianus Marcellinus. The team’s analysis suggests that the recurring droughts may have led to harvest failures and shortages of food, which can help generate instability and violence. The findings were reported in a paper published in the journal Climatic Change. [Continue reading…]