The Crisis of the Third Century: When Rome Nearly Fell

For two centuries after Augustus, the Roman Empire had seemed eternal. The Pax Romana had brought prosperity, peace, and the steady growth of a Mediterranean-wide civilization. The Roman legion had guarded the frontiers from the Antonine Wall to the Euphrates. Trade had flourished, cities had grown, and the Mediterranean had become, for the first and last time, a single unified market. Then, almost without warning, the imperial system collapsed.

Between the assassination of the emperor Severus Alexander in 235 CE and the accession of Diocletian in 284 CE, the Roman Empire entered the most serious crisis in its history. In the space of a single human lifetime, at least 26 men held the title of emperor — most of them soldiers or provincial governors who seized the purple by force — and almost all of them died violently. The empire lost huge territories to invading barbarians and to the resurgent Sassanid Persian Empire. The economy collapsed. The currency was debased to the point of worthlessness. A devastating plague, named after the bishop Cyprian of Carthage, killed perhaps five million people and may have contributed to a serious depopulation. The crisis was so severe that the empire of the late third century was almost unrecognizable as the same state that had been ruled by Marcus Aurelius a hundred years before.

The End of the Antonine Age

The crisis had its roots in the long, slow decline of the Antonine dynasty, the line of emperors that had ruled Rome from 138 to 192 CE. The Five Good Emperors — Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius — had governed with competence, but the system depended too much on the character of the individual emperor. Marcus Aurelius, the philosopher-emperor, had spent most of his reign on the Danube fighting Germanic invasions, and the strain of the wars, combined with the devastating Antonine Plague of 165–180 CE, weakened the empire severely.

His son Commodus, who succeeded him in 180 CE, was a vain, cruel, and incompetent ruler whose reign was a long parade of gladiatorial combats in the arena and arbitrary executions in the palace. He was assassinated on the last day of 192 CE, and the dynasty collapsed. For the next two years, Rome was convulsed by civil war, as the provincial armies of Britain, Pannonia, Syria, and Africa each put forward their own candidate for the purple. The victor was Septimius Severus, the able and ruthless commander of the Pannonian legions, who founded a new dynasty and spent most of his reign on campaign in Africa and Britain. The Severan dynasty lasted less than forty years, and the empire it left behind was weakened, exhausted, and deeply in debt.

The Year of the Six Emperors

In March 235 CE, the emperor Severus Alexander was murdered by his own soldiers on the Rhine frontier, near Mogontiacum (modern Mainz). They had complained that the emperor was too lenient toward the Germanic tribes they were supposed to be fighting. The soldiers elevated their own commander, Maximinus Thrax — a giant of a man, possibly of Gothic or Thracian origin, and the first of the so-called “barracks emperors” — to the purple.

Maximinus was a brilliant soldier but a disastrous emperor. He spent his entire reign on campaign, never once visiting Rome. He taxed the population of the empire brutally to pay for his wars, and after three years he was murdered by his own troops, who were tired of his campaigns and his cruelty. What followed was a nightmare: in the year 238 CE, known as the Year of the Six Emperors, six different men were proclaimed emperor in different parts of the empire. The Senate in Rome elevated two of them in quick succession; the armies of Africa and the East elevated others; the legions of Pannonia proclaimed yet another. The Senate’s candidates were murdered; the Africans and the Easterners were defeated. The victor was the young Gordian III, the 13-year-old grandson of one of the senatorial candidates, who was proclaimed emperor by the Praetorian Guard.

The pattern would repeat itself for the next forty years. Emperors were made and unmade by their own soldiers. Few reigned long enough to consolidate power, and the average reign during the crisis was less than three years. The empire was effectively being auctioned off to the highest bidder in every legionary camp, and the bidders were usually the men with the most troops, not the men with the best policies.

The Sassanid Threat

The external pressure on the empire was, if anything, worse than the internal. The year 224 CE had seen a revolution in the East: the Parthian Empire, the great Iranian kingdom that had been Rome’s rival for three centuries, was overthrown by a native Persian dynasty, the Sassanids. The new rulers, beginning with Ardashir I and especially his son Shapur I, were far more aggressive and far more capable than the Parthians had been. They claimed not just Mesopotamia but the entire eastern Mediterranean, and they set out to take it.

In 260 CE, the emperor Valerian suffered one of the most catastrophic defeats in Roman history. He had invaded Mesopotamia to punish the Sassanids for an earlier invasion of Syria, and was defeated and captured at the Battle of Edessa. According to a legend reported by the later historian Lactantius, Shapur used Valerian as a human footstool to mount his horse, and kept him in captivity for the rest of his life, displaying him to his courtiers as a trophy. Valerian was the first Roman emperor ever to be taken alive by a foreign enemy, and the shock to the Roman world was immense.

The Sassanids exploited their victory to overrun the Roman East. Antioch, the third-largest city of the empire, fell to Shapur in 256 CE. Syria, Cappadocia, and parts of Asia Minor were overrun. The crisis forced the Romans to adopt a new defensive strategy: the construction of a great chain of forts and the abandonment of the old idea of defending the empire on the frontier. The Sassanid threat would last for centuries, and the long Roman-Persian Wars would outlast the empire itself.

The Germanic Invasions

The other great external pressure on the empire came from the north. The Germanic peoples of central and northern Europe — the Goths, the Alemanni, the Franks, the Vandals — were growing in population and in military capacity, and the long peace of the Pax Romana had given them a taste for the wealth of the Roman provinces. From the 230s onward, the Rhine and Danube frontiers came under sustained attack.

In the 250s and 260s, the empire suffered a series of catastrophic defeats. In 251, the emperor Decius was killed at the Battle of Abrittus, fighting the Goths. In 259, the Franks and Alemanni invaded Gaul and Spain, sacking cities and reaching as far as Tarragona. In 267, the Heruli, a Gothic tribe, sailed through the Bosphorus and attacked Athens, sacking the city before being driven off by the local garrison. In 269, another Gothic attack on the empire was defeated at the Battle of Naissus by the future emperor Claudius Gothicus — one of the few military successes of the period. For more on these campaigns, see famous Roman battles.

The empire was so weakened that it began to fragment. In 260, the army in the East proclaimed Macrinus’s successor Quietus as emperor; in the West, the governor of Gaul, Postumus, declared independence and established the so-called Gallic Empire, which would rule Britain, Gaul, and Spain for fourteen years. In the East, the queen of Palmyra, Zenobia, established a separate state that included Syria, Egypt, and much of Asia Minor. The Roman Empire of the third century, for a brief period, was actually three empires.

The Plague of Cyprian

Compounding the military disaster was a pandemic. The Plague of Cyprian, named after Saint Cyprian, the bishop of Carthage who described its symptoms, struck the empire sometime in the 250s and recurred repeatedly for the next fifteen or twenty years. Cyprian described it in horrifying terms: the victims suffered from violent vomiting, diarrhea, inflammation of the eyes, and ulcerations of the throat. The disease was highly contagious, killed the majority of those it infected, and spread throughout the empire. The population of the empire may have fallen by a quarter or even a third during the crisis.

The plague’s identity is debated. It has been variously identified as smallpox, viral hemorrhagic fever, anthrax, or even a particularly severe form of influenza. Whatever it was, it killed soldiers and peasants, priests and prostitutes, Roman citizens and barbarian invaders. The army was weakened, the economy was further disrupted, and the depopulation of the countryside made the food supply of the cities increasingly precarious.

The Collapse of the Currency

The economic crisis of the third century was driven by a collapse of the currency. The Roman monetary system was based on the denarius, a silver coin that had been the standard medium of exchange for over three hundred years. In the early empire, a denarius contained about 4.5 grams of silver. By the reign of Marcus Aurelius, the silver content had fallen to about 2.5 grams. Under the barracks emperors, the decline accelerated.

Emperors who needed to pay their troops and buy supplies had only one source of revenue: the mint. They debased the coinage by reducing the silver content, and eventually by replacing the silver with copper coated in a thin layer of precious metal. The denarius of the late third century contained almost no silver at all, and the antoninianus, a “double denarius” introduced by Caracalla, was almost worthless. By the 270s, the inflation was so severe that prices were doubling every few months. The economic life of the empire was paralyzed. Soldiers refused to be paid in the debased coinage, and the government’s ability to raise and equip armies was severely compromised.

The Empire on the Brink

By the early 270s, the Roman Empire had lost more territory than it had gained in two centuries. The Sassanids held Mesopotamia and threatened Asia Minor. The Germanic tribes had crossed the Rhine and the Danube, sacked cities in Gaul and Spain, and raided as far as Greece. The empire had fragmented into three. The currency was almost worthless. The plague was still raging. The population was declining. The army, the only institution that still held the empire together, was making and unmaking emperors in rapid succession.

It seemed possible, in the 260s and 270s, that the Roman Empire might actually come to an end. It did not, but only because of a remarkable series of soldier-emperors who managed, against the odds, to restore the empire’s frontiers and lay the foundations for its long-term survival.

Aurelian and the Restoration of the Empire

The first of these “restorer emperors” was Aurelian, who ruled from 270 to 275 CE. Aurelian was an Illyrian soldier of humble origin, the finest general of his generation. In a series of brilliant campaigns, he defeated the Alemanni, drove the Vandals back across the Danube, abandoned the province of Dacia to the barbarians, and most importantly reconquered both the Gallic Empire and the Palmyrene Empire. The Roman Empire was once more a single state, although it had lost the trans-Danubian province of Dacia and was permanently smaller than it had been a century before.

Aurelian also built the great Aurelian Walls around Rome, a fortification of more than 12 miles that still forms part of the city’s defenses today. He was murdered in 275 CE by officers who feared his harsh discipline, but the restoration he had achieved was not undone.

The Soldier-Emperors: Tacitus, Probus, and Carus

The emperors who followed Aurelian — Tacitus (275–276), Probus (276–282), and Carus (282–283) — continued his work. They drove the barbarians out of the provinces they had overrun, restored the Roman frontier on the Rhine and the Danube, and even struck at the Sassanids. Probus, perhaps the most successful of the three, was murdered by his own soldiers in 282 CE — a fitting end to a generation of military autocrats.

Diocletian and the End of the Crisis

The crisis finally came to an end with the accession of Diocletian in November 284 CE. Diocletian, another Illyrian soldier, was perhaps the most capable administrator in Roman history. He understood that the empire was too large and too threatened to be ruled by a single emperor from Rome. In 293 CE, he instituted the Tetrarchy, a system of four co-emperors, two senior augusti and two junior caesares, who would rule the empire jointly. The eastern half of the empire was ruled from Nicomedia, the western from Mediolanum (modern Milan), with Italy itself reduced to a middle position. For the full story, see the article on Diocletian and the Tetrarchy.

Diocletian also reformed the currency, replaced the worthless denarius with a new gold coin called the solidus, and organized a massive increase in imperial bureaucracy, in the army, and in the tax system. The empire he left behind in 305 CE, when he abdicated the purple, was very different from the empire he had inherited. It was larger, better defended, better administered, and far more autocratic. It was also, in many ways, no longer the same kind of state. Diocletian’s reforms marked the end of the Principate and the beginning of the Late Empire, the period that would lead, almost two centuries later, to the fall of the Western Roman Empire.

For the broader story, see the complete history of the Roman Empire.