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.

[1] According to Ammianus, the following events occurred: In the winter of 367, the Roman garrison on Hadrian's Wall rebelled and allowed Picts from Caledonia to enter Britannia.

Simultaneously, Attacotti, the Scotti from Hibernia and Saxons from Germania landed in what might have been coordinated and pre-arranged waves on the island's mid-western and southeastern borders, respectively.

[3] The milites areani, the local Roman agents who provided intelligence on barbarian movements, seem to have betrayed their paymasters for bribes, which made the attacks completely unexpected.

Although the chaos was widespread and initially concerted, the rebels had aims simply of personal enrichment and worked as small bands rather than larger armies.

There, he began to deal with the invaders:[3] There he divided his troops into many parts and attacked the predatory bands of the enemy, which were ranging about and were laden with heavy packs; quickly routing those who were driving along prisoners and cattle, he wrested from them the booty which the wretched tribute-paying people had lost.

[9] By the end of the year, the barbarians had been driven back to their homelands; the mutineers had been executed; Hadrian's Wall had been retaken and order had returned to the diocese.

Under Civilis' rule the last of the earlier invaders were temporarily driven out in AD 369,[10] possibly using troops under his own personal command, and a program of civil restoration begun.

The author Francis Hagan utilises the Great Conspiracy as the backdrop for his trilogy of books in the Sabinus Chronicles (The Unquiet Shore, The Reaping of the Sea and The Vengeful Tide).