Crisis of the Third Century

The Crisis of the Third Century was a period of about fifty years, usually dated from 235 to 284 CE, in which the Roman Empire came close to collapse. Foreign invasions, civil wars between rival emperors, epidemic disease and economic breakdown struck at the same time, and for over a decade the empire was split into three parts. It ended with the reforms of Diocletian, and historians often treat it as the boundary between classical antiquity and late antiquity.

The crisis began in 235 when the young emperor Severus Alexander was murdered by his own troops on the Rhine frontier. His successor, Maximinus Thrax, was a career soldier who had risen from the ranks. Over the next half-century the armies repeatedly made and unmade emperors. More than two dozen men held or claimed the imperial title during this period, and most died violently, killed by their own soldiers or rivals. In 238 alone six men held the imperial title. Because each new ruler depended on the goodwill of the army, he had to reward it with money and was constantly pulled away from the frontiers by rebellions.

In the east, the Parthian dynasty had been overthrown in the 220s by the Sasanians, who ruled a more aggressive and centralised Sasanian Empire. Its king Shapur I raided deep into Roman Syria and Anatolia, and in 260 captured the emperor Valerian, who died in captivity, an unprecedented humiliation. On the Rhine and the Danube, new Germanic confederations such as the Alamanni and Franks, and the Goths further east, crossed the frontiers. In 251 the emperor Decius was killed in battle against the Goths, and Gothic fleets later raided the coasts of the Black Sea and the Aegean.

Unable to rely on a distant emperor, regions began to defend themselves. In 260 the general Postumus was proclaimed emperor in the west and created a breakaway state, the Gallic Empire, covering Gaul, Britain and for a time Spain. In the east, the city of Palmyra, under its ruler Odaenathus and then his widow Zenobia, took control of much of the eastern provinces and, from around 270, Egypt as well. The emperor Gallienus, who ruled from 253 to 268, held only the central part of the empire.

From about 249 an epidemic known as the Plague of Cyprian spread across the empire for perhaps two decades, causing heavy loss of life, though its nature and toll are uncertain. To pay their armies, emperors repeatedly reduced the silver content of the coinage. By the 260s the main silver coin contained only a few per cent of silver, prices rose sharply, and the state increasingly collected taxes and paid soldiers in goods. Trade and city life in many regions declined, and towns built new walls.

A series of capable emperors, mostly from the Balkan provinces, reversed the collapse. Claudius II defeated the Goths at Naissus around 268 or 269. Aurelian, between 270 and 275, defeated Zenobia and the Gallic Empire, reuniting the empire by 274. He also built a new wall around Rome and gave up the exposed province of Dacia, north of the Danube.

In 284 Diocletian took power. He enlarged the army, divided the provinces into smaller units, separated civil and military commands, reformed taxation, and in 293 established the Tetrarchy, a system of two senior and two junior emperors. These measures, continued by Constantine I, created a more bureaucratic and militarised state, sometimes called the Dominate, which held together for over a century more in the west and much longer in the east.

Our 200 CE map shows the Roman Empire before the crisis, and the 300 CE map shows it restored under the Tetrarchy, facing the Sasanian Empire in the east.