Commodus period

In 175, a large force of Sarmatian cavalry, consisting of 5,500 men, arrived in Britannia, probably to reinforce troops fighting unrecorded uprisings. In 180, Hadrian's Wall was breached by the Picts and the commanding officer or governor was killed there in what Cassius Dio described as the most serious war of the reign of Commodus. Ulpius Marcellus was sent as replacement governor and by 184 he had won a new peace, only to be faced with a mutiny from his own troops. Unhappy with Marcellus's strictness, they tried to elect a legate named Priscus as usurper governor; he refused, but Marcellus was lucky to leave the province alive. The Roman army in Britannia continued its insubordination: they sent a delegation of 1,500 to Rome to demand the execution of Tigidius Perennis, a Praetorian prefect who they felt had earlier wronged them by posting lowly equites to legate ranks in Britannia. Commodus met the party outside Rome and agreed to have Perennis killed, but this only made them feel more secure in their mutiny.

The future emperor Pertinax was sent to Britannia to quell the mutiny and was initially successful in regaining control, but a riot broke out among the troops. Pertinax was attacked and left for dead, and asked to be recalled to Rome, where he briefly succeeded Commodus as emperor in 192.