Great Conspiracy

The Great Conspiracy was a year-long state of war and disorder that occurred near the end of Roman Britain. The historian Ammianus Marcellinus described it as a barbarica conspiratio, which took advantage of a depleted military force in the province; many soldiers had marched with Magnentius in his unsuccessful bid to become emperor. Few returned, and supply, pay, and discipline in the following years may have been deficient.

It is difficult to ascertain the exact chronology of the events because their main source, Ammianus, was living in Antioch at that time. His information looks second-hand and confused and some is inconsistent with that produced by other sources.