Between the accession of Marcus Aurelius in AD 161 and the death of Constantine the Great in 337, approximately eighty men bore the title of emperor (Augustus), either at the capital or in some other part of the empire. Between 247 and 270 alone thirty emperors were proclaimed. Therein lay one of Rome’s most grievous and expensive problems. Distinctions between emperors on the one hand, and usurpers or pretenders on the other hand, are misleading, for most of the emperors who managed to assert their claims to the throne were just as much usurpers or pretenders as those who failed to do so.
The old custom by which emperors were created by the senate had become a threadbare farce. Throughout the period that body, though still deeply respected, only made two or three attempts to take the lead in establishing the successions, in each case with exceedingly impermanent results.1For emperors were now almost invariably created by one of the armies. When the new Augustus had been acclaimed by his troops, he usually wrote to the senate informing them of his appointment and requesting senatorial approval. Under threat of coercion, the senate agreed, willingly or otherwise according to circumstances. The motives of the armies were selfish; they hoped for the huge gifts which on these occasions were extravagantly provided (p. 49). Since local recruitment was prevalent, they were stronger in parochial esprit de corps than in patriotism. Accordingly, with the backing of the large civilian populations of their areas, they declared new emperors with deplorable frequency; and the ruler whom they superseded was almost always killed.
This totally unstable situation regarding the succession paralysed the empire’s defence system, with correspondingly grave results for its economy. There were constant, costly civil wars; time after time a military effort on the frontiers had to be called off because emperors felt obliged to defend or assert themselves against a rival Roman army commander. ‘What’, as Herodian demanded, ‘was the use of barbarians being annihilated when greater slaughter took place in Rome itself and in the provinces?’ Germans and Persians were, of course, well aware of this situation: how far they acted in collusion with one another is not known, but inevitably they exploited Rome’s internal preoccupations.
On certain occasions, when the troops themselves took the initiative, the commanders had little alternative to assuming the purple, since refusal of the offer would have meant immediate assassination. Occasionally, too, a leader seized power in order to fulfil a local and urgent need to shore up a frontier. But nearly always the lure, however obviously impermanent, was the throne of the Augusti. The result is to be seen today in the extraordinarily large number of different persons portrayed on the coinage. For after a man had been declared emperor, wherever he might be, he had to reward his supporters by an immediate issue of money.
One of his early concerns thereafter was to try, usually in vain, to establish some arrangement about the succession to the throne, in the hope of creating confidence and warding off the almost inevitable blow. There were two ways of doing this. In the first place, like Septimius Severus, Philip, Decius, Valerian and many others, he could rapidly bring forward and promote his own son or sons or some other close relative, so that if the emperor himself died there might be a chance of a smooth take-over within the family. The armies, in theory, liked a dynastic succession of this kind, although their emotional loyalty to the heir often wore off quickly if he proved parsimonious, or too juvenile and inexperienced to make an effective commander. The senators, on the other hand, preferred a second method by which the ruler nominated and adopted a suitable, competent heir from outside the family. For then they could be consulted, and the man proposed for the succession would be some worthy member of their own order—whom they might continue to influence. This adoptive solution was scarcely available to men conducting rebellions on the frontiers. But in Rome, during the stable second century, such methods had been employed to produce four successive emperors of exceptional talent, the last of them being Marcus Aurelius. A century later, Diocletian was a convinced adherent of the doctrine that the emperor should ignore the claims of birth and choose the best man available as his heir, and his elaborate arrangement of the Tetrarchy was based on this principle. Yet the rulers of both periods were to a large extent making a virtue of necessity, owing to the lack of sons of their own; and in both periods again they took the precaution of bringing their adoptive heirs into their own families by marriage.*
After the first of these series of adoptions, Marcus Aurelius designated his son Commodus as his successor. Indeed, following the precedent by which he himself had possessed an imperial colleague (Lucius Verus), he even elevated the young man to be a fellow-Augustus, relying on experienced henchmen to support his claim to the succession. Commodus was the first ruler whose legitimacy and consequent divine favour were derived from his ‘birth in the purple’. Coins and medallions stress his special nobilitas, and when he married in 177 his father issued a medallion dedicated to father and son alike as dynastic founders (PROPAGATORIBVS IMPERII). The youth turned out to be very erratic, or at least so anti-traditional that disaster was inevitable. But whether or not Marcus ought to have known that this would be so, the rejection of his son’s claims in favour of someone else would almost certainly have involved one of the civil wars which were to proliferate so disastrously around future successions.
The murder of Commodus (192) created just such an occasion. The praetorian guard, recalling Its initiatives in the previous century, sponsored two successive emperors who were both killed within five months.2 But meanwhile the provincial armies were taking a hand, and, although the praetorian guard continued on occasion to seek the throne for its commanders,3 this legionary initiative set the pattern for a century. In the Civil Wars of AD 68–9 the legions of Spain, Germany and Syria had put up their rival candidates. In 193 there were similar assertions by the armies of the Danube provinces, Syria and Britain.4 After four years of bloodshed and expenditure, the Danubian candidate, Septimius Severus,* was victorious. On becoming established as emperor he took precautions against future usurpations (like his own) by limiting the total regular force under any one provincial governor to a maximum of two legions.
The Danubian armies were by far the largest in the empire, and during the recurrent civil strife of the third century it was their candidate, more often than not, who gained the throne. A turning-point was reached in 235 when a Danubian unit on the upper Rhine successfully proclaimed a Thracian ex-ranker, Maximinus I. The Danube armies also put forward the usual quota of would-be rulers who failed to establish themselves.5 But in addition to these a whole series of emperors who successfully asserted their claims were themselves Illyrians, originating from Danubian and Balkan territories. Decius, born in this area to a family of Italian origin, had a short reign full of disasters. But Claudius II Gothicus (268–270), Aurelian, Probus, Diocletian and Constantine, all of Illyrian peasant family, were men of exceptional force and military talent who, against all probabilities, staved off the collapse of imperial defence (pp. 33 ff).
The vital frontier provinces, which bound together the western and eastern parts of the empire, were Upper and Lower Pannonia, comprising eastern Austria, western Hungary and northern Yugoslavia. Farther east, Moesia extended to the mouth of the Danube. These were the regions which now produced not only the most able Roman emperors but the best Roman soldiers; and a great many of these soldiers served in the large armies which manned their own territories. Fortunately, they were filled with the frontiersman’s intense Italian, Roman patriotism. They had in their hearts an image of eternal Rome as the inseparable associate of their own homeland—their defence of the Danube frontier simultaneously protected Italy and their own country.
In Pannonia, which supported the bulk of this responsibility, the process of Romanisation had not extended very far beyond the upper class in the towns; and the territory was scarcely Hellenized at all. Before the Romans took over, it had already been launched on a modest economic development, and its artistic monuments continued to show strong regional characteristics. And yet the coinage of Decius, honouring the two Pannonias and the Genius of the Illyrian army, tells how conscious of their specific Roman role and contribution these peoples and soldiers had become. From their stock came few senators, but it produced the officers who were the most powerful element in the army, and with the backing of their compatriots some of them became outstanding emperors of Rome.
The Rhine armies were now smaller and less important than the armies of the Danube. But they had to meet terribly severe German raids (p. 32), and they felt neglected by Rome in favour of the Danube legions, and impeded from carrying out their vital task of defence. It seemed to these officers and soldiers, in a time of grave crisis, that the only solution was to have an emperor of their own. And so they supported Postumus, governor of one of the German provinces along the river, in a rebellion against Gallienus, whose son was put to death by Postumus at Colonia Agrippina (Cologne) (259/60). This revolt was only one among many, but it had particularly far-reaching repercussions. Postumus was joined not only by Gaul but by Britain and Spain, and for a time he even controlled parts of north Italy.6 For fourteen years western Europe was a large separatist state, confronting Rome in a cold war which broke occasionally into open hostilities.
Gallienus issued gold medallions to his own officers and friends, explicitly on account of their loyalty against Postumus (OB FIDEM RESERVATAM). Postumus for his part inaugurated his coinage with a few specific references to German aspects of Hercules – whom he adopted as his divine patron – and with a description of himself as Restorer of the Gauls. This was aimed at increasing Gallic self-consciousness, but thereafter the coins show no trace of a nationalist policy; a later issue calls him Restorer of the World. Postumus saw himself as thoroughly Roman, and at Augusta Trevirorum (Trier) –one of the German business cities that had replaced cities farther from the front as political centres – he set up his own consuls and senate, independent from those of Rome. Racked by external and internal strains, the empire was breaking up into separate parts. Gallienus’ coin-type ‘Peace Everywhere’ and Postumus’ traditional ‘Happiness of the Age’ are both extraordinary examples of wishful thinking.
The uncomfortable dilemma of the central emperor was clearly illustrated by the concluding stages of his relationship with this Gallic empire. In order to hold Postumus off while at the same time maintaining readiness against external threats, Gallienus had set up a mobile strategic force at Mediolanum (p. 39). But this was such an impressive army that its general was a security hazard. Indeed, its very first commander, the capable Aureolus, deserted from Gallienus to Postumus, and was subsequently proclaimed emperor himself (268); and in the same year the next commander of the corps, Aurelian, was one of the leaders of a successful plot to murder Gallienus. An emperor could not command everywhere, and an effective military unit must mean a dangerous rival. The failure to find a solution to that internal problem was one of the principal reasons why the empire seemed doomed to succumb to its external enemies.
After Postumus’ last successor Tetricus had come over to Aurelian during the decisive battle between their armies (274), there were unpleasant aftermaths of these troubles in Gaul. Under Probus two further revolts broke out. Moreover, as had also happened a century earlier, hordes of desperate and destitute men – expropriated peasants and fugitives, and the army deserters who had abounded for nearly a century – banded together under two chiefs who may have had wider ambitions (285–6).7 These gangs were crushed by Diocletian’s colleague Maximian. But immediately afterwards a more serious breakaway in the same western provinces almost repeated the pattern established by Postumus. Carausius, a naval officer of humble sailor origin from the lands of the Rhine-Scheldt estuary, was entrusted by Maximian with the defence of Britain against German pirates, but set himself up as independent emperor there Instead (286/7–293/4).8 He defeated Maximian and secured some measure of reluctant official recognition, which he celebrated on coinage showing himself as co-ruler of the whole empire. Carausius also temporarily controlled north-eastern France, but lost Gesoriacum (Boulogne) to Maximian’s lieutenant Constantius I Chlorus, and was then killed and succeeded by his own chief ministerAllectus. Three years later, Cosistantius brought Britain back into the empire.
Although Carausius, desiring to trade with Frisia and the Rhineland, struck a coin of much better silver than had been seen in the central empire for many years, this British separatist state, like the government of Postumus, favoured slogans which were pronouncedly Roman in style. Carausius was hailed as Restorer of Britain, but there is no nationalist sentiment. A very large proportion of his coins celebrate the Imperial Peace (PAX AVG.) ; and he was no doubt proud of his ability to keep invaders out of Britain. Yet, even if such local rulers had their successes against the barbarians, these internal dissensions within the empire, requiring precautions and battles by one Roman army against another, could only add to the enormous and unprecedented burden of imperial defence.
The east, garrisoned by a Roman force second only to the Danube army in size and effectiveness, was not slow in putting forward emperors of its own choice. Avidius Cassius, governor of Syria and virtual ruler of the east, who at a time when such rebellions were unusual rebelled against Marcus (175), was the protégé of his Syrian compatriots in the eastern armies; and after that revolt the emperor indicated that in future no man should govern the province of his origin. Another Syrian nominee was Elagabalus (218–22). Thereafter a number of emperors were proclaimed by these eastern garrisons,9 including Philip, who was himself the son of an Arabian sheikh (244). Further claimants were backed by the archers of Osrhoene (Mesopotamia), at home or on the other fronts where they were serving.10
But the most vigorous, longstanding and dangerous of these dissident movements was sponsored by that other recruiting-ground for eastern bowmen, the oasis city of Palmyra (Tadmor). Palmyra was strategically placed because it possessed valuable wells and access to a winter tributary of the Euphrates, and was located at a desert crossroads between Syria and Mesopotamia. By the first century BC it had captured the trade between those two countries, and was organising and protecting caravan routes straight across the desert. Annexed by Rome in c. AD 17, the town was subsequently linked by road to the Euphrates (75), and throve on the collection of frontier dues. Since early in the second century it had been occupied by a strong Roman garrison. Septimius and his family staked a good deal on Palmyra. The place was raised to the status of a Roman colony, but the loss of military independence which this change officially entailed meant more rather than less power for Palmyra, since henceforward many of its quasi-autonomous formations of mounted archers were stationed not far from their own city, as important elements in the imperial forces along the Parthian frontier.
When Parthia was superseded by the more formidable Sassanian power (p. 23), the part played by Palmyra in the Roman defence system became indispensable. Psychologically, however, its role was equivocal. It is true that Palmyra favoured certain Greco-Syrian trappings of architecture and costume which looked towards the empire. But its vigorous artistic styles, with their rigid hieratic frontality foreshadowing Byzantium, show a more natural orientation towards Parthian and Sassanian Babylonia and the urban centres of that country, such as Seleucia (Tell Omar) which stood on the Tigris opposite the capital of Ctesiphon (S.E. of Baghdad) and was the third greatest city in the world. Artistic parallels to Palmyra are also to be found farther east still, for example at Shami in the Persian mountains north of Susa.
So, culturally at least, Palmyra was more closely related to the eastern than to the western power. Another reason for good relations with the Sassanians was political: namely their new domination of the river mouths on the Persian Gulf, which endangered Palmyrene trade. So when Shapur I overran Rome’s eastern provinces and captured Valerian (p. 25), the chieftain of Palmyra Odenathus (Odainath) made approaches to the invader (c. 260). But Odenathus encountered a contemptuous rebuff. This was one of Shapur’s mistakes which, despite all his successes, he had good reason to regret. For henceforward Odenathus staunchly supported the Romans. Indeed, in the desperate situation in which Gallienus found himself, the defence of the whole region was very soon in Odenathus’ hands. Supported by his Palmyrene and Osrhoenian archers and by heavy cavalry, he was even strong enough to advance upon the Persian capital and then to repeat the attempt. The vacuum created by Rome’s preoccupations elsewhere gave Palmyra the opportunity to assert its control from the Taurus mountains to the Red Sea. Moreover, Odenathus was virtually in charge of the entire Roman armies of the east. As a challenge to Persia, he was even allowed by Gallienus to call himself King of Kings.11 Moreover, to the annoyance of Roman provincial governors – who regarded him as a barbarian – he was also awarded the titles of Corrector of the Orient, Leader of the Romans and Imperator.
But then Odenathus, turning back from Babylonia to face a Gothic invasion of Asia Minor, was murdered (266/7); and his gifted and erudite widow Zenobia (Bat Zabbai), with the leading Greco-Syrian scholar Cassius Longinus as her chief minister,12 set out to achieve total independence. Indicating her admiration for Cleopatra, she seized Egypt, and most of Asia Minor fell into her hands.13 Zenoia’s possessions extended from Mesopotamia to a point almost within reach of Europe. Then, either just before or just after the accession of Aurelian (270), she disclosed her new plans. Although anti-Roman elements must have been in the ascendant at Palmyra, her son, who had inherited his father’s titles, was in Roman fashion declared Augustus, and she herself became Augusta. Even the Palmyra that now, as a new power, refused to serve Rome any longer could not get clear of the Roman track on which it had so long been running.14
When Aurelian was seen to have accepted the challenge, Zenobia’s propaganda attempted a last minute compromise: her coins give her son his old titles only, and show Aurelian on the other side. But it was too late for such diplomacy, for Aurelian, proclaiming himself Restorer of the East, recaptured Asia Minor and Egypt, and defeated the queen’s leading general outside Antioch and Emesa. Palmyra itself fell to him, rebelled, and fell again. Zenobia, together with Tetricus (the last breakaway ruler of the west), was kept to walk in golden chains in Aurelian’s Triumph. Her city was devastated. To the inconvenience of Rome, which now had to do the work of the caravan police, Palmyra relapsed into the desert village it once had been, until Diocletian made it into a Roman palace city (p. 104).
Between the years 266 and 274 the Roman empire had been divided into three independent parts, with separate rulers at Augusta Trevirorum in the west and Palmyra in the east, while the metropolitan emperor controlled only what lay between the two. Although the western and eastern rulers made contributions to external defence, their threat to the central power seemed to Aurelian, even at a time when every effort was needed on the frontiers, to necessitate his expensive expeditions, first against Zenobia and then against Tetricus. When reunification had with great difficulty been achieved, he at last set out against Persia, which had fortunately been suffering from internal dissensions and therefore did little to help Zenobia. But on the way, like so many before and after him, he succumbed to the dagger of an assassin.
There had been many rebellions and usurpations before, and they continued, particularly in Egypt where Greek or Hellenized writers had long been attacking Rome’s injustice, tyranny, avarice, weakness and bad government, calling its emperors uncultured, lecherous Jew-lovers.15 But in many other provinces, too – and often without any such anti-Roman overtones – similar accounts of subversions and fleeting imperial aspirations could be recorded. Few territories were without their own splinter movements and candidates for the throne. This chaotic, anarchic situation, which Diocletian sought to prevent by doubling the number of provinces and multiplying official emperors (p. 68), was a paralysing handicap the Roman government had to suffer inside its frontiers, while simultaneously facing outwards in order to shoulder the massive and ever-increasing burden of the military activity conceived necessary in the interests of imperial defence.