The following is a list of usurpers in the Roman Empire. The term "Roman usurper" tipically refers to individuals who unsuccessfully claimed and/or attempted to usurp the throne of a ruling emperor. The ancient term was "tyrant" (Latin: tyrannus), which had negative connotation in and of itself. Usurpation was common during the whole imperial era; virtually all imperial dynasties rose to power through usurpation and conspiracies. The "imperial office" established by Augustus never defined an stable system of succession, and emperors often had to rely solely on military power to survive.
In the Eastern Roman Empire (395–1453), rebellion and usurpation were so notoriously frequent (in the vision of the medieval West, where usurpation was rare) that the modern term "byzantine" became a byword for political intrigue and conspiracy. For usurpation in the Eastern Roman Empire, see List of Byzantine usurpers.