The Anarchy: from Caracalla to Diocletian, AD 211–284

For the conqueror of Mesopotamia, the British war of AD 208–211 was a dismal business. The empire’s north-west frontier had been troubled since the 180s AD. Mutiny and civil war had so weakened the army there that Roman commanders had been reduced to bribing barbarian chieftains to keep the peace. Severus would have none of it, and saw as well a chance to get his sons, Caracalla and Geta, away from Rome and toughen them up with some soldiering. His preparations were thorough. Tens of thousands of men were massed on Hadrian’s Wall. South Shields was remodelled to hold a three-month grain supply. A fleet was assembled to transport men and stores up the east coast of Scotland. As the army marched, new roads were cut through forests, causeways laid across marshes, bridges thrown over rivers. Perhaps it was just too thorough, for the tribesmen avoided pitched battle and waged guerrilla war. The struggle was already in its third year when Severus died, and the chances of decisive victory seemed remote. The Romans had failed in these northern wastes before, retreating under Domitian in the 80s AD, and again under Marcus in the 160s AD. Elsewhere, too, campaigning outside the limits of plough-cultivation, in the mountains, forests and deserts beyond the frontiers, they had often found themselves in a military morass. We do not know what advice the two young emperors were given by the generals after Severus’s death, but some surely doubted the wisdom of the war. It probably looked unwinnable. The Highlands were hard to control. The tribes were desperately poor. There was little booty. Meantime, the army, its prestige compromised by failure, was thousands of miles from Rome, the Balkans and the eastern frontier. That was dangerous. Whatever was said, Caracalla and Geta would have needed little encouragement to pack for home. They made peace with the Caledonian tribes, dispersed the field army, and returned forthwith to Rome.

Severus had named his sons joint heirs, and on his deathbed had enjoined them not to quarrel. But deep hatred divided them. They travelled separately on the journey home, kept separate courts within the palace, and even discussed splitting the empire in two. The matter was resolved when Caracalla had his brother murdered – stabbed to death by army officers, it is said, having fled through the palace into his mother’s arms. Caracalla went immediately to the Praetorian Barracks to secure the allegiance of the Guard. ‘With you I pray to live or, if need be, die,’ announced the emperor, though he wisely added, ‘Yours are all the treasures of the state’(6) – specifically, higher pay and better rations. Then he went to the Albanum Barracks, where the legion his father had stationed near Rome was based. At first the gates were closed against him, but, again, an offer of higher pay promptly secured the soldiers’ allegiance. Soon, around the empire, frontier legionaries were being assembled on their parade-grounds to be told of the army pay-rise, to damn the traitor Geta, and to swear devotion to Caracalla. Many stone-cut records of these events, so-called ‘loyalty inscriptions’, have been found at army bases. Meantime, Geta’s friends and allies were destroyed in a savage purge (one source inflates the total slain to 20,000).

Insecurity and inflated spending were hallmarks of Caracalla’s reign. The power of the internal security apparatus – essentially an empire-wide network of military police and paid informers – was increased. The army pay-rises were underwritten by hefty tax increases. The inheritance and manumission taxes paid by Roman citizens were increased from 5 to 10 per cent, and Caracalla’s famous citizenship edict of AD 212, by which all free persons in the empire became citizens, was intended to increase the numbers obliged to pay. Aurum coronarium – the ‘coronation gold’ traditionally paid only on the emperor’s accession and often in practice remitted – became a recurring extraordinary levy. The coinage was debased: a new double-denarius was issued at a lower weight (and therefore silver content) than the two denarii it supposedly represented. All these schemes transferred surplus from civil society to the state and its army. By these means the cost was met of the military-bureaucratic complex over which Caracalla presided: not only army pay-rises and rewards to favourites, courtiers and loyalist officers; also the ‘bread and circuses’ and monumental building that appeased and awed the mob; and the bribes and subsidies to border chieftains that were a growing feature of imperial defence.

Once things were settled in Rome, Caracalla spent his time with the army, fighting first in Germany (AD 213), then in the East (AD 215–217). His methods were a mix of vanity, intrigue and brute force. Modelling himself on Alexander, he adopted Macedonian dress, created a 16,000-strong phalanx, and tried to fix up a marriage alliance with an eastern princess. He employed secret diplomacy to buy off potential enemies and isolate the more intractable. His armies were then free to crush, successively, German tribesmen, Egyptian tax-rebels and Parthian garrisons. Even so, the emperor did not inspire confidence, and his position was gravely weakened in the winter of AD 216–217 when he ordered a retreat in the face of an impending Parthian counter-offensive. Caracalla was assassinated by a common soldier in April AD 217.

For a moment the grip of the Severan dynasty was broken. The eastern army hailed one of its own generals emperor. But Macrinus ruled for only a year. He succumbed in June AD 218 to a military revolt orchestrated by the leading women of the ousted House of Severus. Though Septimius’s widow, Julia Domna, was dead, her sister, Julia Maesa, was very much alive, and her two daughters, Julia Soaemias and Julia Mammaea, each had a son – and therefore a ‘legitimate’ Severan heir. Determined to maintain the pre-eminence of the family, Julia Maesa roused her Syrian supporters to revolt (she was from the eastern city of Emesa), bribed the soldiers to overturn Macrinus, and placed one of Septimius Severus’s two great-nephews on the throne.

The ‘Syrian’ faction were unfortunate in their chosen instrument. Elagabalus, who had taken the name of the eastern sun-god of which he was chief priest, was a religious fanatic. Established in Rome from early AD 219, he continued to don the fantastic garb of an eastern priest, filled the court with a retinue of religious charlatans and cranks, and ordered the Senate to elevate the cult of the Unconquered Sun into the principal state religion. In the bizarre theocratic dictatorship of Elagabalus, devotion was the principal qualification for high office, and an actor became Praetorian Prefect, a charioteer headed the Night-watch, and a hairdresser supervised the corn-supply. Accounts of the fertility ‘rites’ enacted at court lost nothing in the retelling in Rome’s salons and bars. By the summer of AD 221, Julia Maesa was manoeuvring to destroy her grandson and replace him with his less colourful cousin. The blow fell in March AD 222. The Praetorians were bribed, Elagabalus and his mother murdered, and the rest of the court hunted down and killed. The theocratic dictatorship collapsed in a day, and Severus Alexander was hailed emperor.

The principal qualities of the new emperor were that he was a relatively ‘normal’ Roman youth, he was easily controlled by his female minders, and he was not Elagabalus. Even so, the Syrians were discredited and had ground to make up; behind the cardboard ruler they schemed to rebuild their power. The tension that had recently developed between the traditional aristocracy of office represented by the Senate and the military-bureaucratic complex of court and army recruited from the Equestrian Order was eased. Senators were readmitted to the highest councils of the state, and previously reserved equestrian offices – crucially that of Praetorian Prefect – were opened to them. The mob, too, was courted in the usual way, with handouts and public works. Court expenditure, on the other hand, was reined back, and new taxes were levied on the rich. The Syrians were eager to make themselves popular.

The real danger, however, was not at home but abroad. Decisive shifts in the balance of geopolitical power were taking place in both the East and the North. The military monarchy had effected a significant redistribution of resources from civil society to the state, and an enlarged and reorganized army had enabled it to crush domestic and foreign enemies. But, locked into an eternal military struggle with her neighbours, Rome could only ever gain temporary respite through her victories; indeed, these very victories provided the spur to her enemies to regroup, rearm, and return to fight again. Severus’s conquest of Mesopotamia in AD 197– 199, and Caracalla’s successful defence of it in AD 215–217, had shattered the cohesion of the fast-decaying Parthian Empire. In the 220s AD it had splintered into rebellious provincial fragments. Among the local potentates who then contended for power was one Artaxerxes, Prince of Persepolis, ancient homeland of the Achaemenids, who, 500 years before, had ruled the greatest empire on earth. After smashing the Parthian king in pitched battle in AD 227, Artaxerxes overran Mesopotamia and reached the borders of Syria and Asia Minor in the succeeding three years. As the new ‘Great King’ or ‘King of Kings’, Artaxerxes laid claim to the empire of his ancestors – a domain that had embraced the whole Eastern Mediterranean as far as the Aegean. The wreckage of empire wrought by Severus’s legions a generation before had produced its Nemesis. The spirit of Cyrus, Darius and Xerxes walked again: an aggressive, boasting, thrusting imperialism that mirrored that of Rome: the Sassanid Empire.

Severus Alexander’s attempts to negotiate were ignored, and Roman forces had to be rushed to the East. The campaign was mismanaged and losses were heavy on both sides. Both empires, too, were soon distracted by more pressing problems elsewhere, and the war, which had begun with such grandiose aims in AD 230, had petered out by AD 233. But the relocation of the court to Antioch, and the shift of crack Danubian units to the East, had gravely weakened the empire’s European defences. German tribes penetrated the frontier screen and plundered territory along the Rhine and Danube. Such news cannot have played well in the ranks of soldiers recently transferred from the Balkans to the East: their families and farms at home had been exposed by their absence fighting a ‘foreign’ war. When court and army relocated again to the North, the centrifugal tensions within the Roman state came to a head. Severus Alexander was eager to cut a deal with the tribes. His mother, Julia Mammaea, wanted to escape the miserable northern forests. The court – or so it seemed to some – was run by women and stuffed with foppish eastern favourites. The ‘Germans’ had had enough of the ‘Syrians’. In March AD 235 the Danubian soldiers acclaimed one of their own emperor: Maximinus Thrax, Maximinus the Thracian, a huge peasant-soldier who had risen from the ranks to top command. The eastern troops panicked and fled. Severus Alexander and his mother were murdered in the base-camp at Mainz.

Maximinus (AD 235–238) represented the military monarchy in its most extreme form. A farmer’s son from a Balkan village, he was a rough career-soldier who had lived his whole adult life in the army. Immediately threatened by plots, one organized by a group of senatorial officers, another by eastern generals, the opposition was ruthlessly crushed. The candidate of the Rhineland and Danubian legions, he then went onto the offensive in the North, smashing the German tribes in pitched battle. Agents, meantime, were dispatched across the empire to rake in revenue to support the war effort. Within just three years, these policies had provoked a fresh revolt.

The military monarchy was falling apart, the state sinking into anarchy. The enemies of the empire were growing stronger. Current tax revenues were inadequate to support the size of army required to keep them out. Legions, in consequence, had to be constantly shifted to deal with one emergency after another. Such redeployments frequently created new openings that led to localized collapses and the devastation of Roman territory. This in turn undermined the cohesion of the imperial ruling class, which fragmented into regionally based factions, each eager to concentrate revenues and soldiers in defence of local territory. Centrifugalism become an inherent feature of the empire in decline, and the attempt of successive regimes to suppress it further undermined imperial defence by diverting troops to internal security.

For the rich landowners of Roman Africa, the German tribes might as well have been on the moon. When the financial procurator threatened aristocratic estates in his efforts to fill the emperor’s war-chest, he provoked a property-owners’ revolt. A group of young bloods assassinated the procurator and declared emperor an octogenarian nobleman of impeccable pedigree and distinguished service currently serving as provincial governor. Gordian I (AD 238), acting with a vigour that belied his age, immediately dispatched a band of armed partisans to Rome to overthrow the government, while appealing to the rest of the empire for support. All save Spain, Dacia and Pannonia declared for Gordian – a measure of the fear for person and property engendered by the brutal Maximinus regime. But the property-owners’ revolt was a castle of sand. The civilians could not defeat the army. Just 22 days after it began, the revolt in Africa was over, and both Gordian I and his son – named co-emperor and therefore recorded by history as Gordian II – were dead.

In Italy, at first, matters took a different turn. Here the Gordianic faction was headed by an energetic provisional government dominated by senators: the so-called Board of Twenty. Exploiting widespread hostility within the military to the dominance of the German faction, the Board had been busy turning paper support into armies. Undeterred by the setback in Africa, they now elevated two of their own number, Balbinus and Maximus, to the throne. Then, in response to protests from soldiers and the mob against the restoration of senatorial rule, they added a third: Gordian I’s 13-year-old grandson, who thus became Gordian III. Meantime, the regime prepared to meet the onslaught of Maximinus’s legions. The Board of Twenty’s show of force was promptly rewarded. Maximinus was held at the fortified city of Aquileia on the north-east coast of Italy. Unprepared for a long siege, he quickly ran out of food, at which his soldiers mutinied, murdered him in his bed, and transferred their allegiance to Gordian III (AD 238–244).

For a moment it appeared that, against the odds, the civilians had won. A property-owners’ revolt against the demands of the military monarchy had produced a government of senators in Rome. It was an illusion. The military were the dominant partners in the victorious faction and they had no intention of sharing power: the Praetorian Guard murdered Balbinus and Maximus, dumped their bodies in the street, and declared Gordian III sole emperor – an event signalling the true collapse of the property-owners’ revolt. A military monarch – and his minders – again reigned supreme.

The German and civil wars had weakened the frontier defences. In the East especially, from which the army had marched off to Germany in the winter of AD 233–234, the situation was dire. The Sassanids had invaded Syria and were within reach of Antioch. Though a Roman counter-attack mounted in AD 243 was spectacularly successful, the army’s logistics broke down, the troops went hungry, and an ambitious general, Philip the Arab, seized his opportunity to incite the troops against the boy-emperor and have him murdered. The fates of Maximinus Thrax and Gordian III revealed a new feature of the anarchy. The soldiers had grown accustomed to making and unmaking emperors. They expected their leaders to keep them well supplied, to lead them to victory, to safeguard the interests of the army. When they failed to do so – as they often did in the troubled times of the mid 3rd century AD – they found themselves at the mercy of serial mutineers.

The reign of Philip the Arab (AD 244–249) exemplified the whole nexus of contradictions that had produced the anarchy. Peace was made with the Sassanids only to be followed by three years of war on the Lower Danube, where new enemies, peoples migrating from the depths of Eurasia, were pushing against the frontiers of the Empire. Then, while celebrating the apparent return of peace on Rome’s one-thousandth birthday in AD 248, the regime was hit simultaneously by three army revolts – on the Danube, in Cappodocia, and in Syria – and a new invasion by Carpi, Goths and Vandals on the Lower Danube. Lack of money was at the root of all these conflicts. The Danube revolt had been triggered by arrears of pay, the eastern revolts by ruthless tax-collecting, the barbarian incursions by failure to pay a promised subsidy. It was a classic ‘scissors’ crisis: in one place mutiny and invasion over payments not made, in another revolt against revenue collection. Here, in a sense, is written the whole history of the decline and fall of Rome.

The man sent to restore order on the Danube drove out the barbarians and paid the soldiers their arrears. They responded by acclaiming him emperor, and though the general tried to decline and protested his innocence to Philip, he was hopelessly compromised and found himself propelled willy-nilly into a struggle for power. It was Philip, however, who was defeated and killed when the two armies clashed, and Decius Trajan (AD 249–251) became emperor. Decius was unusual among 3rd century emperors in being a distinguished senator linked by marriage with an old Italian aristocratic family. His relations with the Senate were therefore cordial. He could not, however, eschew military affairs; to base oneself in Rome and rule as a civilian politician was no longer an option. It was again the Goths on the Lower Danube who posed the principal threat. The barbarians had crossed the ice-bound river in force during the winter of AD 250–251. The city of Philippopolis had been captured and put to the sack. But when Decius engaged the Gothic host in a great battle in the marshes of the Danube Estuary, he was betrayed by one of his own subordinates. The details are obscure. It appears that two of the enemy’s battle-groups had been repulsed, and Decius was advancing to attack a third, expecting support from the force commanded by Gallus, Governor of Moesia. But Gallus made no move as Decius’s men marched into a bog and were destroyed by Gothic archery. The emperor’s body was never found. Gallus (AD 251–253) was proclaimed in his place. Had the traitor done a deal with the Goths? Or had he merely sensed an opportunity in the chaos of battle? Whatever, the incident seems evidence of deep rottenness within the Roman state. In the succeeding two decades, it would bring the Empire close to collapse.

Gallus did not last long. He seems to have been paralyzed by indecision in the face of Gothic raiders, a new Sassanid offensive in the East, and a severe epidemic of plague. By the winter of AD 253–254 the frontier legions were in revolt. Gallus was defeated by Aemilianus and the Danube army, and then murdered by his own troops. But Aemilianus (AD 253) reigned for just three months before he was deserted and murdered in his turn, as the soldiers switched allegiance again, this time to the usurper Valerian, marching on Italy at the head of the Rhineland army. The anarchy was fast accelerating into a chaos of warring factions. The Roman imperial elite was imploding even as its enemies poured across crumbling frontier defences. The end of the empire seemed possible. In response to escalating crisis, a critical decision was taken by the new regime. The political order would be adapted to reflect the centrifugalism now endemic in the overextended empire. Valerian (AD 253–260) appointed his son Gallienus (AD 253–268) co-emperor, first with the junior rank of Caesar, later the more senior one of Augustus. Shortly afterwards the empire was effectively divided in two, with the East allocated to Valerian, the West to Gallienus. Henceforward there were two courts, two armies, two centres of power, one facing the Sassanids in the East, the other the barbarians in the North.

Valerian went out to the East in AD 256 or 257. Establishing his headquarters at Antioch, he first repelled a Sassanid incursion under Shapur I, then turned to deal with a new threat on the coasts of Asia Minor, where Borani and Goths were mounting seaborne raids. But the expedition had to be aborted when plague broke out in the army and, at the same time, news arrived that Shapur had returned to the offensive. Shifting front yet again, Valerian marched into Mesopotamia, hoping, by devastating his enemy’s territory, to force upon him a negotiated peace. Little else was possible, for the Roman forces were at their limit. Barbarian raiders threatened in the rear. The communication lines were long and exposed. The army was withered by plague, climate, battle casualties and garrison duty. Shapur agreed to negotiate, but then, treacherously, seized Valerian, who died soon afterwards in Sassanid captivity (AD 260). Though a victim of deceit, Valerian had been driven to destruction – driven to take the risk that led to his destruction – by military weakness.

Gallienus could offer no assistance from the West. The Rhine defences had collapsed completely in AD 258. The Franks broke through in the north and overran much of Gaul and Spain. The Alamanni attacked in the south and invaded Italy over the Alpine passes. The following year, Carpi, Goths, Marcomanni, Quadi and Sarmatians assailed the Danube line, while rebel legions declared against Gallienus in the Balkans. Battling to restore control here – partly by ceding territory to King Attalus of the Marcomanni in return for his allegiance – Gallienus lost the western portion of his territory. The military collapse on the Rhine, at a time when the emperor, fully committed on the Danube, could offer no help, triggered a civil war. Officers and landowners in Germany, Gaul, Spain and Britain rallied around the usurper-emperor Postumus. Gallienus’s belated efforts to suppress the revolt were beaten off, and the rebels quickly consolidated their territory into a secessionist ‘Gallic Empire’, destined to endure for 15 years. A complex military crisis had thus exploded across the Western Empire in AD 258–259, destroying its political and military coherence. Simultaneous pressure at several points on his overextended lines had exhausted Gallienus’s diplomatic and military resources, leading to multiple breakthroughs on the frontier. This in turn had shattered the unity of the western ruling class as regional fragments abandoned allegiance to the central Empire and reorganized in their own defence.

Meantime, with no support from the West, the eastern Roman generals were unable to save Antioch, the ancient capital of Syria and one of the greatest cities of the Empire. A makeshift emergency government was then constructed by the eastern generals around two young usurper-emperors. Gallienus opposed this move: he had lost the revenues and legions of half the West; now he was threatened with the loss of the whole East; he risked being reduced to a Balkan-based rump as he faced the barbarian hordes massed along the Danube. Macrianus, the leading Roman general in the East, and the two eastern emperors, who were his sons, marched west to confront Gallienus, but they were defeated and killed somewhere in the Balkans. Macrianus’s eastern colleagues, on the other hand, succeeded in defeating Shapur and driving the Sassanids back. This left the Eastern Roman Empire intact and, for the moment, relatively safe for the rebels, since Gallienus could hardly contemplate an invasion of Asia. Instead he sought an ally: a client-ruler rich and powerful enough to act as an effective counterweight to both the Sassanid Empire and the rebel regime: Odenath of Palmyra.

A great trading city on the northern edge of the Arabian Desert, Palmyra had grown rich on the caravan trade passing from Mesopotamia to Syria; it was a vital link between the Mediterranean and the Orient bringing highly prized luxuries like perfume, spices and fine textiles to Roman markets. Palmyra, however, was a society under stress. The Sassanids coveted the wealth of the trade routes. Incessant warfare had disrupted the caravans. The Romans were no longer able to protect their allies. So the traditional caution of traders preoccupied with making money had given way to a brooding hawkishness in the city. The potentate of Palmyra had declared himself a king and built an army. Palmyrene gold, after all, could buy many soldiers. Odenath had already seen off a Sassanid army. The city had therefore become a player in the power-politics of the age – one important enough to be noticed and courted by a Roman emperor based in the distant Balkans. Gallienus, in return for an alliance, recognized Odenath as King of Palmyra and declared him Duke of the Roman East. Thus legitimized, Odenath went on to the offensive, winning over many Syrian cities, for whom he now appeared the most promising protector, and capturing Emesa, capital of the embryonic Eastern Roman Empire, whose leaders were promptly put to death. Soon the King of Palmyra was effective master of the Roman East.

The Palmyrene Empire was no mere bubble. It had expanded to fill the vacuum left by the collapse of Roman political and military power in the East, and it was now sustained by the tribute from a hundred fabulous cities. But it was rather less than the super-state that Odenath, dizzy with success, now took it to be. Like others before him who had possessed Syria, he could not resist the temptation of Oriental conquest, and now hurled his army into Mesopotamia. Though knocked back at first, the Sassanids later rallied and repelled the Palmyrene invaders, while far in Odenath’s rear Gothic raiders, seizing the moment, attacked Asia Minor and penetrated as far as Cappadocia. In the winter of AD 266–267, his royal prestige tarnished, Odenath was assassinated in a court plot by a Palmyrene nationalist faction eager to assert independence from Rome. Zenobia, Odenath’s former second wife, henceforward ruled as regent on behalf of her infant son Waballath. Gallienus refused to recognize the new regime, but his attempt to suppress it militarily was defeated. The embattled Balkan emperor had tried to prop up imperial authority by cultivating an eastern client-state. But Roman power was so hollowed out that nothing had remained in the East to contain the client-state’s expansion and hold its rulers in check. Now the Kingdom of Palmyra, like the Gallic Empire in the West, stood independent of Rome.

The Gallic emperor, indeed, had played much the same role in the history of the West in the 260s AD as the Palmyrene king in that of the East. Gallienus’s forces had been kept at bay, and domestic usurpers suppressed. The Franks and Alamanni had been expelled, and the Rhine defences restored. The coasts had been secured against seaborne raiders. The currency had been improved and commerce revived. The property-owning classes and the cities of the West had been given good reason to remain loyal. Gallienus meantime remained hopelessly embroiled in the Balkan inferno. AD 262 was an especially black year, as a new wave of plague swept across the empire, and the Goths devastated Thrace, Macedonia and Greece. By forced marches the emperor crossed and recrossed his shrunken domain, plugging one gap only to find another had swung open in his rear. The Goths were no sooner expelled from the Balkans than they were attacking Asia Minor, where they captured and plundered the great city of Ephesus, already racked by earthquake and plague. In AD 268 the barbarians came again in massive force, both Heruli and Goths, attacking by land and sea, sweeping aside local Roman forces, plundering at will the cities of the Aegean. This time Gallienus caught and smashed them in pitched battle – but it was to be his last fight.

The general Gallienus had left to guard Italy had risen in his rear. The emperor raced back to confront the rebels, putting Milan under siege, but some of his own officers too were traitors, and when the emperor rode out alone to reconnoitre a reported enemy sortie, he was assassinated. The empire he left behind seemed on the edge of the abyss. The West was controlled by Gallic emperor Victorinus, the East by the Palmyrene regent Zenobia, Italy by a third rebel regime. The North was threatened again by Alamanni and Goths. Earthquake, plague and war had devastated the empire. Taxation, requisitioning and compulsory services were crushing. The treasury was empty, the currency worthless. When the Balkan army chose Marcus Aurelius Claudius – Claudius Gothicus, as he would become known – to be the new emperor, many must have wondered whether he might not be the last. Yet, despite everything, this Balkan army, all that now survived of the once-mighty Roman imperial state, represented a kernel of military power that was uniquely strong – a nucleus about which the empire could still be reconstructed.

The forces ranged against Rome were still highly disparate and localized. They lacked organizational coherence, transcontinental reach, any real vision of an alternative world. The Roman ruling class – or rather the high command of the military monarchy that formed its inner core – retained such resources of centralized political and military power that the greatest of disasters could still be set right. The barbarians could invade and raid while the emperor’s war-machine was distracted, but they could not hold ground when it returned. Equally, rebels could carve out a regional domain when the legitimate emperor was fully committed against foreign invaders, but he, needing the resources of a united empire, was bound to come for them sooner or later. That is why usurpers usually attacked the central empire: the political game they played was, in the long run at least, an all-or-nothing gamble. Unless destroyed by foreign enemies – and they were yet too diffuse – the empire, however much divided, tended to re-cohere. Regionalism was still counterbalanced by a yet more powerful centralism.

The military monarchy, moreover, under the stress of war during Gallienus’s long reign, had become tougher. Senatorial generals had finally disappeared completely; all senior officers were now professional men of equestrian status promoted from the army’s ranks. The senators had also lost control of many provincial governorships, again to equestrians. The central state’s military-bureaucratic complex was expanding at the expense of an established civilian aristocracy that had once monopolized high office. An in-service staff college had emerged for promising centurions who were in training for higher (equestrian) commands. Many new mounted regiments were raised (called simply equites), and the old mounted detachments of the legions were reconstituted as independentunits (called promoti). The idea was to create a field-army with an elite core of fast-moving, hard-hitting shock cavalry. The military dominance of the heavy-infantry legions, the basis of Roman military power since the 6th century BC, was over. To fund the reformed army, the state operated an emergency finance regime. As well as heavy – sometimes crippling – levels of taxation, requisitioning and labour services, deliberate debasement of the currency effected a direct transfer of wealth from civil society to the military-bureaucratic complex. In AD 235 the silver content of the denarius, the basic Roman monetary unit, had been 1.3 gm; by AD 253, it had fallen to 0.8 gm; by AD 268, it was reduced to 0.1 gm – the state, in other words, was melting down coins collected in taxation, increasing the base-metal content, and reissuing an increased number with the same nominal value.

Gallienus had pared the military monarchy down to its essence. After him, a succession of three great soldier-emperors from the Balkan army – Claudius Gothicus (AD 268–270), Aurelian (AD 270–275) and Probus (AD 276–282) – used this streamlined instrument to restore, stone by stone, the edifice of imperial power. First, Claudius Gothicus re-established control over the empire’s central zone by overthrowing the usurper regime in Rome, ejecting Alemannic invaders from northern Italy, and breaking up a massive Gothic onslaught by land and sea against the cities of the Aegean. The emperor then succumbed to plague. He was succeeded by his second-in-command. Aurelian maintained the momentum of the counter-offensive in the West. Having finished with the Goths on the lower Danube, the emperor turned his attention to the upper Danube, under attack from several Germanic confederations. Taken by surprise, the emperor suffered defeat at Placentia in northern Italy, a setback which immediately prompted revolt in Rome by senators opposed to the rule of the soldier-emperors. The rebels had moved too soon. The Germans were crushed in two big battles, and few of the raiders escaped home. Aurelian then marched on Rome and smashed the revolt. While there in AD 271, convinced of the imperial capital’s chronic vulnerability, he ordered the construction of one of Late Antiquity’s greatest monuments. The Aurelian Wall around ancient Rome was 19 km long, 3.6 m thick, and 6 m high. It had 18 gateways, the four main ones double-arched, and both here and at regular intervals around the circumference there were square projecting towers. The work, which continued for years, was carried out by slaves and conscripts. The monument symbolized the empire’s insecurity, its great reserves of strength, and the subordination of its once pampered citizens to the dictates of a war-economy.

Zenobia meantime had openly thrown off Palmyra’s formal subordination to Rome. Aurelian anyway wanted to restore the flow of eastern tax revenues to the central treasury. Shifting the bulk of his Balkan army to the East, he planned a two-stage offensive to collapse the Palmyrene Empire: first the outlying territories of Egypt and Asia Minor, only loosely held in thrall by Palmyra, were to be wrested back; then the Syrian heartland would be stormed. The plan was sound. The presence of the emperor with a strong army restored the confidence of the eastern cities in Roman power. A lenient policy towards reformed rebels encouraged rapid realignment. The professional skill of Roman generals in combined-arms operations soon gave them mastery of the battlefield. The Palmyrenes depended for success on the charge of elite units of super-heavy cavalry – so-called ‘cataphracts’, where the rider was encased in armour, and sometimes his horse as well. Lighter, faster and highly trained, Aurelian’s Danubian and Moorish cavalry would fall back before the cataphracts, drawing them forwards, wearing them out under the heat of a Syrian sun, breaking up their close-order formation. The Roman infantry provided a solid defensive line. The Roman cavalry would then launch decisive counter-attacks when their opponents’ exhaustion and disorganization were at a peak. Antioch fell. Then Emesa. Zenobia withdrew to Palmyra itself. The Romans closed in, bribing local tribes to desert, beating back a Sassanid relief force. Famine broke out in the city. As her empire disintegrated, Zenobia fled. Palmyra then surrendered on terms. Zenobia’s leading counsellors were tried and executed. She was caught, spared, and kept for display in a later Roman triumph. The Palmyrene Empire had collapsed in a year (AD 271–272). Though a fresh nationalist revolt brought Aurelian racing back the following year, it was easily crushed; and this time the city was put to the sack.

Then Aurelian turned to deal with the western secession. The Gallic Empire had, in fact, entered its terminal crisis some years before. The succession to Postumus had been contested, and Victorinus had soon been killed. Tetricus reigned as the third Gallic emperor in just three years. Spain had returned to its former allegiance. Provence had also been lost. Now the Germans were on the offensive, and Tetricus was unable to keep them out. The Gallic Empire thus lost its raison d’être – its superior ability to defend property – and local support fell away. Aurelian, momentarily free of commitments elsewhere, chose this moment to attack, and he emerged victorious from a long and bloody battle at Châlons when Tetricus himself deserted to the enemy and his army broke up in confusion (AD 273).

When Aurelian returned to Rome in early AD 275 to celebrate a double triumph over the Palmyrene and Gallic Empires, he took the title ‘Restorer of the World’ (Restitutor Orbis). It seemed no exaggeration. Aurelian’s were the greatest victories since the time of Septimius Severus. They had achieved one of the most complete turnarounds in Roman history: from the brink of complete disintegration in AD 268 to an empire reunited behind secure frontiers in AD 274. More than that. The financial crisis was eased as the army returned to barracks and tax revenues flowed in again from East and West. The currency was reformed. Debts were cancelled. Corn doles resumed. The Tiber was dredged and its banks restored. The cult of Sol, the Roman Sun-god, was promoted as a supreme state religion, the divine embodiment of the resurrected empire. Aurelian, the soldier-emperor risen from the ranks of Gallienus’s Balkan army, was now father of his country, an old-style Caesar, a true popularis.

Ambition lured Aurelian back to the East in AD 275, this time to launch an aggressive war to recover Mesopotamia. He never had his chance. A petty palace squabble exploded like a bomb and blew Aurelian’s court to pieces. An official accused of lying tried to protect himself by fabricating a capital prosecution list that included several leading officers. They in turn murdered Aurelian in self-defence. The conspiracy had no wider basis, and the army high command, having no desire to upset the Aurelianic system, deferred the decision about a successor to the Senate. The latter, equally wary, prevaricated. Renewed pressure on the frontiers soon forced an appointment, but the reigns of Tacitus (AD 275–276), an elderly senator, and Florianus (AD 276), a close relative, were messy and short. The army quickly reasserted its authority when the Aurelianic frontier settlement came under threat, and Probus, formerly Aurelian’s right-hand man, succeeded.

Probus (AD 276–282), third and last of the great Balkan soldier-emperors, successfully defended the restored Aurelianic Empire. He, like his predecessors, spent almost the whole of his reign on campaign, fighting Germans in the Rhineland, Vandals on the Danube, Nubians at the southern limits of Egypt, bandits in rural Turkey, and new usurper-emperors in the former Gallic Empire.

Despite his energy – perhaps, in a sense, because of it – Probus was brought down by a mutiny in the Balkan army in AD 282. The soldiers assassinated their emperor in protest against being put to work on land reclamation and other public works. The leader of the coup, Praetorian Prefect Marcus Aurelius Carus, was destined to reign only briefly, however. Having made his two sons Caesars, he left Carinus in charge of the West, and himself headed east in company with Numerianus. Yet again, the allure of eastern glory drew a Roman emperor to Mesopotamia; for the Balkan soldier-emperors of the 270s and 280s AD that allure was a curse. Probus, like Aurelian, had been planning a great eastern war when he was killed, and now Carus, though his army captured the Sassanid capital at Ctesiphon, was suddenly struck down, perhaps by a freak accident, perhaps by foul play. His son was murdered soon after. So the Balkan generals, as they had done so often before, convened an army council to decide the future of the empire. Again they chose one of their own to lead them: an Illyrian soldier of modest birth who had risen through the ranks to the command of the household troops: Gaius Aurelius Valerius Diocletianus. We know him as Diocletian. He was one of Rome’s greatest emperors. Elevated on 17 November AD 284, he reigned for over 20 years, after which he voluntarily stepped down, later to die peacefully in his bed. Though no one could have known this at the outset, his accession marked the end of Rome’s long crisis, its decades of anarchy, and inaugurated a period of concentrated reform and political consolidation which amounted, in effect, to a Late Roman counter-revolution.

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