The Crisis of the Third Century (also known as the "Military Anarchy" or the "Imperial Crisis") is a commonly applied name for the crumbling and near collapse of the Roman Empire between 235 and 284 caused by three simultaneous crises: external invasion, internal civil war, and economic collapse.

The changes in the Roman world's institutions, society, economic life and eventually religion were so profound and fundamental, that the "Crisis of the Third Century" is increasingly seen as the watershed marking the difference between the classical world and the world of late antiquity.During this period, the empire is ruled by roughly 20 to 25 individuals, the exact number being a matter of debate as so many claim the title at the same time.

Most of them are prominent generals who assume imperial power over all or part of the empire, only to lose it by defeat in battle, murder, or death, ruling on average only 2 to 3 years.