P. C. Regalianus, also known as Regalian, was Roman usurper for a few months in 260 and/or 261, during the Crisis of the Third Century, a period of intense political instability in the Roman Empire. Regalianus was acclaimed emperor by the troops along the Danube river, a region of the empire that frequently experienced barbarian raids, probably in the hope that he might be able to secure the frontier.

Decebalus, sometimes referred to as Diurpaneus, was the last Dacian king. He is famous for fighting three wars, with varying success, against the Roman Empire under two emperors. After raiding south across the Danube, he defeated a Roman invasion in the reign of Domitian, securing a period of independence during which Decebalus consolidated his rule.