On a spring morning in AD 235, a column of dust on the horizon signalled the approach of Maximinus Thrax’s mutinous troops. On the parade ground in what is now Mainz in Germany, the young emperor Alexander Severus begged his soldiers to fight for him against these rebels. In spite of their promises, renewed the day before, the troops refused to take up arms. They shouted various complaints: against the cowardice of the emperor’s commanders and household, against the rapacity and miserliness of his mother.


When the rebels came into sight, they called out, urging their comrades in arms to abandon the “timid little boy tied to his mother’s apron strings”. Terrified out of his wits, Alexander fled for his imperial tent. There, waiting for his executioners, the 26-year-old emperor clung to his mother, weeping and blaming her for his misfortunes.

Although the contemporary writer Cassius Dio thought the empire had already descended to an “age of iron and rust” (meaning decay) no one could have predicted the chaos that would be unleashed with the murder of Alexander – and the installation of Maximinus as his successor. Since the battle of Actium in 31 BC, when the first emperor, later to be called Augustus, had secured his rule, the Roman empire had known relative security. In over two and a half centuries from then there had been only two protracted outbreaks of civil war: the year of the four emperors in AD 68–69 (two were assassinated and two committed suicide); and the struggles against the emperors Didius Julianus, Niger and Albinus, which brought Septimius Severus to the throne in AD 193.

Although some battles had been lost against external enemies, notably the Germans in the Teutoburger Wald late in the reign of Augustus (AD 9) and the Dacians in the Balkans under Domitian (84–89), the empire had suffered no great defeats. No emperors had been killed or captured by barbarians.

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Trajan had added Dacia, north of the Danube, as a province (101–06) and, apart from relinquishing some briefly held gains in the north of Britain under Domitian and in southern Mesopotamia under Hadrian, no territories had been lost. Internally it had been a time of political stability. Leaving aside ephemeral pretenders, there had been only 28 emperors in 266 years. Statistically the average reign had lasted nine and a half years.

After Alexander’s killing, the age of iron and rust became much worse. The first civil war erupted three years later in 238. There were further outbreaks in 249 and 253. In the 260s armed usurpation became near continuous. By the end of that decade much of both the west and east was held by rival emperors and thus lost to the central government.

Incursions by peoples from beyond the frontiers increased in number and severity. The first Roman emperor to be killed by barbarians in battle was Decius who fell to the Goths in 251 (the Persians’ boast to have killed one of Decius’s predecessors, Gordian III, in 244 was contested by Roman sources).When the Persians captured Valerian in 260, he became the first emperor to be taken alive by an external foe. It was claimed his captor, Shapur, used Valerian as a footstool to mount his horse, and on Valerian’s death had his flayed skin stuffed, and hung in the chamber where Roman ambassadors were received.

In this period the Roman empire suffered its first significant territorial loss, when it abandoned Dacia in the 270s. Given the prevalence of revolt between 235 and 284, any list of emperors must be provisional. Yet at a conservative estimate, at least 30 men held the throne in the 49 years between 235 and 284 – an average reign of a little over 18 months.

What had gone so wrong? We can seek answers in three areas: two concern long-term relations with peoples outside the empire, and the third the role of the emperor within his own society. In all of them it can be argued Rome was the author of its own misfortunes.

A head for a stage prop

When Roman forces reached the Euphrates in the 60s BC, they met the Arsacid dynasty of the Parthians, which had been expanding westward for over two centuries. The understandable, if mistaken, Roman perception that their new eastern neighbour posed a serious threat was reinforced when the Parthians crushed the unprovoked invasion of the triumvir (part of a three-way Roman ruling alliance) Crassus at Carrhae in 53 BC. Having used Crassus’s head as a stage prop in a production of Euripides’s Bacchae, the Parthians subsequently raided Rome’s eastern provinces (40 BC), and, having been expelled, they defeated a campaign of retribution led by Mark Antony (36 BC).

Grande Ludovisi sarcophagus, front marble relief depicting battle between Romans and Ostrogoths
A marble relief depicting a battle between Romans and Ostrogoths. (De Agostini Picture Library/Getty Images)

Although diplomacy often was preferred to conflict when Rome was under the rule of the emperors, several major wars broke out between the two empires. Of these it is significant that only one (AD 162–66), in the joint reign of Marcus Aurelius and Lucius Verus, was instigated by the Parthians. The other four, under Trajan (114–16), Septimius Severus (194–95, 197–98), and Caracalla (217), were begun by the Romans. So it was not so much that Rome had a Parthian problem, more that Parthia had a Roman one.

The campaigns of the emperors Trajan, Lucius Verus and Septimius Severus broadly followed a pattern. The Roman army advanced down the Euphrates, took and plundered the Parthian capital of Ctesiphon, then withdrew. While resulting in no lasting gains, these invasions, above all the repeated sacking of Ctesiphon, did much to weaken the prestige of the Arsacid dynasty, and thus pave the way for its overthrow in the 220s by one of its own client kings, Ardashir of the house of Sasan.

The Persian Sassanid dynasty proved far more aggressive than its predecessor. Ardashir and his son Shapur launched repeated attacks upon Roman territory. Likewise their forces appeared more effective. The Sassanids defeated several Roman field armies in open battle, and, unlike the Parthians, had the capacity regularly to take fortified cities. Archaeology reveals the final siege of the fortress city of Dura-Europos on the Euphrates. By destabilising the dynasty of Parthia, quite unintentionally Rome had been complicit in replacing a reasonably pacific eastern neighbour with one far more lethal.

When the Roman historian Tacitus, in his book Germania, surveyed the barbarian world beyond the Rhine just before AD 100, he saw a myriad of small tribes. Egalitarian in their poverty, they lacked settled political leadership. Their warriors were without armour, and in most cases swords, and the war-band any tribe could put in the field lacked both numbers and organisation.

Yet, by the time Alexander Severus was murdered in the early third century, the ‘barbarians’ north of Rome’s borders had changed – and the Roman empire appears to have been the chief catalyst. Although many small, independent tribes remained, the first large Germanic confederations had emerged: the Franks in the north, the Alamanni beyond the headwaters of the Rhine and Danube, and the Goths by the shores of the Black Sea. These confederations’ forces appear to have been larger, better equipped, and more subject to command and control.

From across the imperial frontiers, the Germans adopted improved farming techniques, the two crop rotation system, and iron ploughshares. Increased agricultural productivity allowed for population expansion. Having the empire as a neighbour stimulated trade, especially in slaves. This probably encouraged aggressive war-making among the already bellicose Germanic tribes.

Some barbarian war leaders will have expanded their territory at the expense of others. Also the flow of wealth generated by trade will have accumulated unevenly, the bulk going into the hands of leaders and their hearth-troops (bodyguards). This would have had the effect of stratifying German society, leading to the emergence of stronger leadership and a proto-nobility.

Two Roman policies accelerated the processes of change. Although the primacy of the legions draws attention away from the practice, Roman armies hired large numbers of mercenaries from beyond the borders. When a troop surge was needed for large-scale campaigning, it was cheaper and quicker to buy in warrior manpower from outside than to recruit and train within the empire. These barbarians served in their own units, often commanded by their own leaders. At the end of their term they returned to their homes, taking with them experience of the more sophisticated tactics and operating procedures of the Roman army. Notoriously, Arminius, the victor in the battle at Teutoburger Wald, had served as an officer in the Roman auxiliaries and had equestrian social status.

Some Roman leaders tried to subdue free Germania. Augustus sent army after army across the Rhine, until the Teutoburger Wald disaster, and the imperial prince Germanicus replicated this in the reign of Tiberius.

Later the emperors Marcus Aurelius (in the second century) and Maximinus Thrax (in the third) were credited with plans to conquer as far as the northern ocean. But most emperors opted for a policy of diplomatic subsidies to favoured leaders, backed with the threat of force aimed at the more recalcitrant to keep the tribes quiescent and divided.

The influx of wealth from imperial diplomacy aided the growth of Germanic confederations. Rome found it easier to deal with more secure leaders of larger units –though, in the long term, this created potentially more dangerous enemies.

Recent archaeological studies offer a potentially new and important insight. From AD 162–80 Rome was embroiled in the Marcomannic wars against the peoples across the upper waters of the Rhine and Danube. From this period, finds in Scandinavia begin to increase both in wealth and in the numbers of Roman imports, including swords. The epicentre was the burial site at Himlingoje on the Danish island of Zealand.

The spread of artefacts, especially elaborate brooches (rosette fibulae), from Himlingoje to other sites in modern Scandinavia, Poland, and the Baltic countries suggests the appearance of a large political unit around the shores of the Baltic Sea. It has been argued that Rome employed diplomatic gifts and the supply of weapons to create an extensive client kingdom beyond the Marcomanni and its other enemies. Not only could the new power based at Himlingoje threaten the rear of Rome’s enemies, but it could supply new reserves of mercenaries.

If the hypothesis is correct, the new extended political organisation could have acted as a model for the soon-to-emerge confederations of northern barbaricum. The leaders of the Franks, Alamanni and Goths could have learnt from the royal dynasty of Himlingoje.

In the north, as in the east, by different processes, but to the same result, Rome had assisted in the creation of enemies much more dangerous to its own empire.

Yet often the greatest threat came from within the empire itself. The first emperor, Augustus, had, after all, come to power by civil war. The Roman empire has been described as an autocracy tempered by the legal right to military revolt. Once voted the correct titles – including maius imperium (military authority) – the victor in a civil war was as legitimate as the man he had replaced.

All emperors needed to monopolise military success and glory. All was well if the empire faced war on only one frontier: the emperor went to the war zone, and the result, more often than not, was a victory. If the campaign was a failure, however, the emperor could be seen to have shown himself as unfit for his role, and in the third century his troops might have overthrown him.

Problems also arose if there were wars on two fronts, and the reigning emperor lacked an adult son or other close relative to despatch to face the second threat. If a general was sent out who was not a member of the imperial family, and he did well, his soldiers might consider he had showed the right stuff to be emperor, and proclaim him. The resulting civil war would strip troops from the frontiers, which would encourage further barbarian incursions. Any local commanders who won victories against these new attacks might in turn be acclaimed emperor, leading to yet more civil conflict, and thus yet more external attacks. The basis of the role of the emperor contributed to the creation of a vicious circle of war, foreign and domestic.

A map showing the Roman empire in AD 235–38
Our map shows the Roman empire in AD 235–38. In the preceding 250 years, Rome had, for the most part, enjoyed stability and territorial expansion. Yet in the following century, it was to be plagued by civil wars and raids by external aggressors. (© Martin Sanders)

The power of four

Diocletian, who came to the throne in 284, was of lowly origins and lacked a formal higher education, but he came up with an answer that had eluded his predecessors. First, in 286, he appointed an old comrade in arms, Maximian, as co-Augustus. Then, in 293, he co-opted two junior imperial rulers, Constantius and Galerius, as Caesars.

The tetrarchy (rule of four) formed a college of emperors. As the empire had three frontiers facing high intensity external threats (the Rhine, Danube and the east), a member of the imperial college would be available to each, with one member in reserve.

Diocletian intended the tetrarchy to be self-perpetuating. In 305 he and Maximian retired. Constantius and Gallerius stepped up to the rank of Augustus, and two new Caesars were appointed.

Yet the tetrarchy was not a permanent solution. Maximian had been reluctant to retire, and promptly attempted to reclaim power in 306. Civil war returned during the fourth century. But Diocletian had temporarily broken the vicious circle and bought the empire a vital breathing space.

Fifty years before Diocletian’s rise to power, Alexander Severus’s mother was said to have summoned the Christian thinker Origen to the imperial court. At the time, Christianity was a fringe religion, yet over the next half-century it was to experience a dramatic change in fortunes.

Many Romans knew that the well-being of their empire rested on the Pax Deorum, the right relations between Rome and the pagan gods. With the chaos of the third century, it was clear something had broken down.

Christians, of course, denied the existence of the pagan gods and so, to the majority of the population, they were atheists. The troubles of the empire demonstrated that the gods were angry, and the cause of their displeasure might be found in the presence of atheist Christians within the empire.

Previously, with the exception of Nero, all persecutions of Christians had been localised and ‘bottom up’. A specific catalyst – a flood, drought, or similar – had led the population of pagans in the area to begin lynching and denouncing their Christian neighbours.

To keep order the Roman provincial governor had had to step in with official arrests and trials. In the face of a tumult of war and usurpation, this no longer seemed enough. In 249 the emperor Decius ordered that all the inhabitants of the empire should sacrifice to the traditional gods. In 257 the emperor Valerian commanded the first empire-wide persecution explicitly aimed at Christians. The following year he issued further, tougher instructions.

It was the fate of these first two imperial persecutors that catapulted Christianity to prominence. Decius was the first emperor to be cut down by barbarians in battle, and Valerian was the first to fall into their hands alive. Christians exulted, and it must have given even the most traditional Roman pagan cause for reflection. It seemed that the god of the Christians had demonstrated both his existence and his power, and he had taken revenge on those who raised their hands against his followers.

The Roman empire had survived the age of iron and rust, but those who had gained most were the Christians.

Dr Harry Sidebottom is a historian of ancient Rome.


This article was first published in the September 2014 issue of BBC History Magazine