Crisis of the Third Century
A period of political upheaval, civil war, economic disruption, and external invasions that weakened the Roman Empire from 235 to 284 CE.
Year of the Six Emperors: The Roman succession crisis of 238 CE, when six men were recognized as emperor during a year of revolt and civil war. Its rapid succession of rulers exposes the instability that defined the wider crisis.
Gallic Empire: A breakaway Roman state in Gaul, Britain, and parts of Hispania that existed from 260 to 274 CE. Its separation shows how military emergencies enabled regional rulers to challenge Rome.
Severan dynasty: A Roman imperial dynasty that ruled from 193 to 235 CE, ending with the assassination of Severus Alexander. Its collapse in 235 conventionally marks the crisis's beginning.
Diocletian: Roman emperor from 284 to 305 CE who reorganized imperial government and restored central control. His accession conventionally closes the crisis, while his reforms addressed its recurring instability.
Roman military: The armed forces of ancient Rome, organized into legions, auxiliary units, and other formations. Armies increasingly made emperors and decided succession through force.
Palmyrene Empire: A short-lived eastern Roman breakaway state led by the Palmyrene rulers, reaching its height under Zenobia. Its expansion into Roman territory exposed the empire's weakened eastern control.
Caracalla: Roman emperor from 211 to 217 CE, known for extending citizenship to nearly all free inhabitants of the empire. His citizenship grant broadened the imperial community while increasing demands on administration and taxation.
Tetrarchy: The system established by Diocletian in which four rulers shared responsibility for governing the Roman Empire. It was designed to improve succession and govern an empire too large for one ruler alone.
Roman imperial succession: The processes and power struggles through which authority passed from one Roman emperor to another. The absence of a settled succession rule turned military loyalty into a recurring political contest.
Battle of Edessa: A battle in 260 CE in which the Sasanian king Shapur I captured Roman emperor Valerian. The emperor's capture marked an extraordinary military and political humiliation for Rome.