The Year of the Six Emperors was the year AD 238, during which six men made claims to be emperors of Rome. This was an early symptom of what historians now call the Crisis of the Third Century, also known as Military Anarchy or the Imperial Crisis (AD 235284), a period in which the Roman Empire nearly collapsed under the combined pressures of barbarian invasions and migrations into the Roman territory, civil wars, peasant rebellions, political instability (with multiple usurpers competing for power), Roman reliance on (and growing influence of) barbarian mercenaries known as foederati and commanders nominally working for Rome (but increasingly independent), the devastating social and economic effects of the plague, debasement of currency, and economic depression. The crisis ended with the ascension of Diocletian and his implementation of reforms in 284.

The Praetorian Guard (Latin: Cohortēs praetōriae) was a unit of the Imperial Roman army that served as personal bodyguards and intelligence agents for the Roman emperors. During the Roman Republic, the Praetorian Guard were an escort for high-rank political officials (senators and procurators) and were bodyguards for the senior officers of the Roman legions. In the year 27 BC, after Rome's transition from republic to empire, the first Emperor of Rome, Caesar Augustus, designated the Praetorians as his personal security escort. For three centuries, the guards of the Roman emperor were also known for their palace intrigues, by which influence upon imperial politics the Praetorians could overthrow an emperor, and then proclaim his successor as the new Caesar of Rome. In AD 312, Constantine the Great disbanded the cohortes praetoriae and destroyed their barracks at the Castra Praetoria.