Defence measures were needed on many borders, but the only major foreign power among Rome’s enemies had long been its eastern neighbour. Until the third century AD semi-feudal Iranian Parthia, under its ruling house the Arsacids, controlled Iraq and Persia and, more loosely, some of the lands to Persia’s north and east. The Parthians adjoined the Roman empire along the Euphrates, and this, too near the Mediterranean for comfort, was the most sensitive part of Rome’s oriental frontier.16
Although actual hostilities, accompanied as they were by vast expense, only occupied about one-sixth of the time, the relations between the two empires were perpetually strained. The Parthians raided Syria, and Rome, where there was always a militaristic party urging emperors to behave like Alexander the Great, launched a considerable number of invasions into Parthian territory. Sometimes these were disastrous; at Carrhae (Haran) Crassus lost his army and his life (53 BC). Sometimes, on the other hand, the expeditions appeared to be successful. For example Trajan captured the Parthian capital Ctesiphon and Seleucia across the Tigris (AD 115) (and even presented the Parthians with a monarch, REX PARTHIS DATVS, p. 22). But such successes, though very costly in men and money, were always short-lived in their effects. The only lasting solution would have been the total destruction of one of these powers by the other, and this was beyond the bounds of military and financial possibility.
The general aim of Roman policy was to control the northern dependencies of Parthia. For a long time the major bone of contention was the huge mountainous land of Armenia, which without clearly defined frontiers extended to the north of Mesopotamia as far as the Caucasus, while its western flanks around the upper Euphrates adjoined the extremities of the Roman empire. Each of the two empires, for centuries, invaded Armenia and fomented internal revolutions there, so as to have a puppet monarch who would serve its policy and prestige; and each also continued to feel that an Armenia belonging to the other was a dagger pointing at its own heart. But in spite of all these exertions neither side ever achieved its purpose for more than fleeting durations. Diplomatic settlements, such as those attempted by Augustus and Nero, had to be cautiously handled, because important sections of public and aristocratic and military opinion in Rome required not an equal settlement but victory. The designs of imperial coins make it clear that gloryweighed more heavily than practical advantage. Indeed, an emperor who proved unable or unwilling to pursue large-scale frontier warfare might soon be killed by his own side, as the fates of at least three emperors showed.17 And so attempts at a diplomatic solution were rare, cautious and impermanent in their results.
Meanwhile it was becoming evident to Roman leaders that the key to the conquest of the Armenian highlands and to the elimination of Parthia as a major power was Mesopotamia. By this was meant not the whole land between the Euphrates and Tigris but its north-western region, which now comprises parts of Iraq and Asiatic Turkey. That area, which had been colonised extensively by the heirs of Alexander the Great, formed an important political and commercial link between Syria and the deserts beyond. Furthermore, its occupation would enable Roman forces, first, to advance half-way to the leading Parthian cities without leaving their own possessions, and secondly to invade Armenia from two sides instead of from one. Accordingly Trajan annexed the country as a new province of Mesopotamia, and took over Armenia, not in accordance with normal policy as a puppet kingdom but as a further Roman province. This convinced imperialist also annexed Assyria (Adiabene) beyond the Tigris, and gave the southern part of the land between the rivers a puppet ‘King of the Parthians’. His intention was that these should be protective outpost areas beyond the main lines of defence. But when Trajan died, Hadrian decided that such annexations were no solution to the problem, and reverted to the old idea of a buffer state of Armenia ruled by a pro-Roman monarch. Another client-king was to be supported on the throne of Mesopotamian Edessa (Urfa), the capital of Osrhoene immediately beyond the Euphrates. Hadrian may have been right to decide that the permanent control of Mesopotamia would be too expensive to be practicable. For Parthians could move upstream to invade the area with the protection of the desert on their right, but it was hard for Romans, who were not in possession of the Persian mountain ranges beyond, to maintain the occupation of such a province. Nevertheless, since Hadrian did not feel able to relinquish control altogether, his decision meant a reversion to the constant nagging warfare of previous centuries.
When Parthia launched one of its periodical coups d’état in Armenia, the governor of Marcus Aurelius’ Anatolian frontier province Cappadocia was defeated and killed, and Marcus felt obliged to send his colleague Lucius Verus to direct a series of large-scale campaigns (163–6). As before, the Parthian capital met with destruction, and Edessa was re-established as a protectorate. It was probably at this stage that the Romans captured, fortified and garrisoned Dura (Salahiye), situated on the Euphrates a little below its tributary the Khabur. This originally Greek but now largely Parthianised town, a melting-pot of many languages and artistic styles, now became the southern frontier post of Rome’s Mesopotamian province.18 However ultimately inconclusive, the fighting had at least brought a peace which lasted for nearly thirty years.
Hostilities broke out again when the Parthians, profiting by Roman civil war, invaded Mesopotamia in 195. Three years later the Romans, under Septimius, sacked the enemy capital yet again, and, although he could not capture the Arab desert-fortress of Hatra, the province of Mesopotamia was reannexed. At least four settlements of Roman exsoldiers were planted in order to hold the region down. The historian Dio Cassius, though no enemy to Septimius, criticised these expensive efforts at conquest.19 But Caracalla, obsessed by a desire to rival Alexander the Great, took the opposite view. These ambitions also gave him the idea, original for a Roman emperor, of marrying the daughter of the Parthian king, Artabanus v. But that monarch did not fancy the suggestion, which consequently became one of history’s might-have-beens. Caracalla reverted to the usual plans for conquest, assisted, in this case, by the kidnapping of the kings both of Edessa and of Armenia. Caracalla crossed the Tigris into Assyria, but before the campaign could develop further he was murdered (217). His successor Macrinus presented the Armenian diadem to Parthia’s nominee; this was so pacific and sensible that it probably contributed to his desertion by his own troops, and subsequent execution.
But now there occurred, to Rome’s lasting disadvantage, one of the decisive events of the age. During the previous century Parthia had been declining in strength. The process was accelerated by its warfare against Rome, and particularly by the invasion of Septimius.20 Such recurrent crises weakened the hold of the Parthians over their feudal dependencies. Among these was Persepolis, whose prince Ardashir (Artaxerxes), ruler of a large area extending from the Persian Gulf to Isfahan, now invaded Parthia and overthrew Artabanus v,21 setting up throughout the entire empire his own Sassanian dynasty, named after his grandfather Sassan (223/6).
The capital of the new régime was still Ctesiphon, but its holy city was at ancestral Istakhr near Persepolis. Nearly eight centuries earlier, when the glorious Achaemenid Persians had displaced the Medes, the centre of power had shifted from northern Iranian tribes to southern princes; and now the pattern repeated itself. Sassanians were eager to emphasise this ancient inheritance, and yet their institutions and culture also took over a great deal from their immediate Parthian predecessors. But the new state was far more formidable than Parthia. In spite of continuing Greek influences, the abandonment of Greek models for the new empire-wide coinage was a sign of intensely nationalistic policies.22 Centralisation was greatly increased, both in the powerful, intolerant state church and in the government. The Sassanian monarchs built up a stable bureaucracy and, while respecting the ancient families, created a new and powerful class of lesser nobles directly dependent on the crown.
Establishing closer and more fruitful relations with the peoples of outer Iran, they saved the Greco-Roman world from the nomad hordes compelled to remain outside their far-off northern and eastern frontiers. Like the Romans, they were subject to barbarian pressures on their borders; and like them again, they were from time to time immobilised by internal dissensions. Nevertheless their heightened efficiency confronted Rome with a military threat at least as dangerous as anything that the very largest concentrations of Germans could provide, and probably more perilous still because of superior Persian coordination. For the Sassanian army, reinforcing the traditional mail-clad horsemen by recruitment from new nobles, was the most up-to-date attacking force of the age. The Romans paid it the compliment of imitation (p. 39), but they had lost the chance either of reducing their eastern neighbour to insignificance or of bringing it to a workable settlement. Rome’s eastern military activities, hitherto something of a luxury, had now become a grimly urgent and immensely expensive necessity.
For the Sassanians were not only powerful; they were also aggressively inclined to expansion. Claiming the restoration of the ancient Persian frontiers, they interpreted this to require the absorption of all Roman territory as far west as the Aegean sea. Such was the menace which the young Severus Alexander, by no means a military expert, had to encounter. Although the desert fortress of Hatra, which was now garrisoned by Roman troops,23 held out against the Sassanians, Ardashir overran Mesopotamia (230), and there were mutinies among Rome’s eastern garrisons. Severus Alexander attempted an ambitious three-pronged invasion. Suffering severe casualties from the climate, his armies were less than successful. Yet their losses were matched by Persia’s, and the Mesopotamian province was temporarily reannexed. But only six years later, in the time of Maximinus I, it was overrun again, and Nisibis (Nüsaybin) and Carrhae fell into Persian hands.
The full, unprecedented burden which would now fall upon Roman armies began to be clear when Shapur I (Sapor) (?239–70) was crowned with the provocative title of ‘King of Kings of Iran and non-Iran’. Next to Hannibal, Shapur was the most dangerous enemy Rome ever had. In addition to yearly raids into the Roman provinces, he launched three major campaigns, the first in the time of Gordian III (242/4), the second at some date between 250 and 256, and the third which brought the reign of Valerian to an end (259 or 260). Shapur’s account of what happened, engraved in three languages at Naksh-i-Rustam near Persepolis,24 differs from anything we learn from the scrappy accounts of Greek or Roman writers. But his claim to have captured thirty-seven cities is probably justified. The Mesopotamian towns that fell into his hands included Carrhae, Nisibis (?c.254), Dura (255/8),25 Edessa (c. 260) and Hatra. Shapur recorded a major victory over the Romans at Barbalissus south-east of Aleppo. Moreover, not only Mesopotamia but also Armenia was lost to Rome. Shapur even captured Antioch, certainly once and possibly twice,26 and in retaliation for Trajan’s ‘king given to the Parthians’ he set up a puppet Roman emperor there. He even took Caesarea (Kayseri) in Cappadocia, devastating both Asia Minor and Syria with a roughness which suggests that, despite his claims, he did not intend their permanent annexation. This ferocity discouraged the enemies of Rome from welcoming Shapur’s leadership. Although he was reputed to be brave, liberal and interested in the things of the mind and spirit, he made mistakes; another was his rejection of the proffered assistance of his strongest potential ally in the region, Palmyra (p. 19).
Five Persian reliefs carved on the mountainsides of Fars show three Roman emperors in various degrees of defeat and degradation.27 Roman coins, on the other hand, continued at intervals to report victories. But the young Gordian 111, as unqualified for warfare as Severus Alexander before him, lost his life in Mesopotamia during a Persian campaign (244). Shapur, on one of his monuments, shows Gordian in a prostrate position, implying he fell in battle; or his own troops may have lynched him. There was also a strong suspicion that Philip, his praetorian prefect and successor, was responsible for his death. In any case Philip did not fight on. He arranged to retain the Mesopotamian province, but tacitly abandoned Armenia and paid Shapur a considerable sum of money. Although there were advantages in this course, Mesopotamia was not easy to hold without Armenia, and it was a penalty of diplomacy that the Persians chose to regard his action as implying recognition of their claims; the relief which shows Gordian as fallen displays Philip as a suppliant. But far worse was the fate of Valerian, who fell into Shapur’s hands. The traditional story tells of a Persian trap, though there remains the alternative possibility that he was taking refuge from his own mutinous army. Together with many soldiers who were settled by the Persians and made to work for them, Valerian remained permanently their prisoner. This event, the most inglorious in all Roman history, is emphasised over and over again in Persian propaganda. Valerian’s son Gallienus either did not succeed in rescuing him or did not try. His father’s name and memory were obliterated from the records.
After the death of Shapur, the Sassanians retained Armenia and Mesopotamia, but internal troubles caused their impetus to weaken. For example, they took little effective advantage of Palmyra’s breakaway from Roman rule (p. 20). When Palmyra had been brought to heel, the emperor Carus recaptured the Mesopotamian province and seized the enemy capital, but soon succumbed to lightning or more probably conspiracy (283). Then the Persian king Narses (293–302) declared war against Rome, defeated Diocletian’s lieutenant Galerius, and recovered Mesopotamia.28 However, a subsequent important victory by Galerius in Armenia, which resulted in the capture of Narses’ wives, forced the Persians to abandon the newly gained territory and sue for peace. The treaty confirmed Rome’s claim to the region, not quite as far as the precarious old southern frontier of Dura but down to Circesium (near Bassira), which still remained the border in Mohammedan times. The Romans had temporarily regained the superiority, and Narses was obliged to recognise their spheres of influence in Armenia and the Caucasian lands to its north.
Still, however, the settlement was not permanent. The old tug of war was renewed, though now with the larger Roman forces which the strength of the Sassanian power necessitated. Shapur II (310–79), a strong monarch after a period of internal confusion, was provoked by Armenia’s conversion to Christianity into occupying the country, but soon lost it again to a young relative whom Constantine placed on the Armenian throne. But this new policy of keeping the country directly under the imperial dynasty was not successful, and the struggle over both Armenia and Mesopotamia continued. Armenia was partitioned (384/7), but in the seventh century each territory fell to the Moslem Arabs, who succeeded to the control of Sassanian Iran and of the eastern parts of the Byzantine empire – gravely weakened as they were by a relationship of cold war, sometimes breaking into open hostilities, that had lasted for seven centuries.
The frontier was heavily guarded. Along the desert border, which ran through Palmyra and Bostra to Petra, Diocletian built or reconstructed powerful forts with square towers and posterns, served by new roads and arms factories.29 Farther to the north also, where the land between the great rivers was divided between Romans and Sassanians, there were powerful Roman defences. A massive earthwork extended, with some interruptions, for 470 miles. The Persian side, too, had elaborate fortifications; this was a sealed-off barrier between two worlds. And yet the peoples on either side of the boundary had a great deal in common – and wherever the line was fixed the same would have been true. Indeed the emperor and king themselves would have recognised many similarities in the elaborate etiquettes of one another’s courts, and during rare moments of comparative friendliness they spoke of one another as Brothers. Yet each side rejected peaceful relations (with their possibilities of a luxury trade that Palmyra, Petra and Alexandria would have welcomed), in favour of this prolonged confrontation.
While the Parthians were ruling, there had been an element of the war-game in this; campaigns trained the Roman troops and gave the emperors honorific titles and applause. But when the Sassanian monarchy came to power, the war-game turned to deadly earnest. Even after Rome’s traumatic experiences at the hands of Shapur I had subsided into the old bickering for Armenia and Mesopotamia, the fact that the enemy had become so much more powerful cost the Romans, for evermore, huge and unprecedented sums, both in ordinary everyday defence and in the much larger expeditionary forces which were periodically needed to maintain and stabilise the position.
These were the largest armies which Rome ever mustered. In order to attain such a size, they had to be supplemented by troops from the northern frontiers. But, whenever an emperor felt obliged to call such forces away from the Danube and the Rhine, the tribes beyond those rivers could take advantage of their withdrawal and confront the Romans with war upon two fronts at once.
Apart from two advanced bulges or bastions-the Agri Decumates beyond and between upper Rhine and upper Danube, and Dacia on the other side of the lower Danube – the principal northern boundary of the empire consisted of those two rivers.30 Facing the easterly reaches of the border were independent Dacians, a people of Thracian origin, and tribes belonging to the large Iranian group of the Sarmatians – effective archers, and creators of the superb animal art of the steppes which is particularly evident in this area. Beyond almost all other points on the frontier, as also in many regions within its limits, the inhabitants were Germans. These were to be found across the whole western length of the river barrier, from Aquincum (Budapest) to the mouth of the Rhine.
The principal gods of the Germans were concerned with war. Yet these peoples were also familiar with agriculture and stock-raising31 and, although lacking in town-life and liable to internal dissensions, had worked out orderly systems of administration which gradually reached a certain size. Such governments were controlled by kings or groups of leaders, who were more or less dependent on the Assembly (Thing) of their tribe. Tacitus expressed the view that the freedom of the Germans was a deadlier enemy to Rome than the despotism of the Parthians. But this menace only became serious during the second century AD, when the German tribes began to show themselves capable of coordinating their activities in larger confederations or coalitions. A good deal of gold came into their hands, partly from individuals who had served Rome, partly through cross-border trading relationships, and partly because the Romans liked their frontiers to be fringed by a cordon sanitaire of semi-dependent states which they were prepared, despite the unpopularity of this course in certain circles at home, to subsidise.
At first, the critical area for the Romans had been the Rhine boundary. In the second century AD the danger-point was the Danube, which now had a garrison of ten Roman legions compared with four on the Rhine. Restlessness across the river came to a head in the time of Marcus Aurelius, causing a series of events which permanently transformed the empire. For during a long period of relative stability, the numbers of the Germans had outgrown their relatively simple agricultural techniques. They were land-hungry and wanted to abandon their marshy forest clearings for richer country within the frontier. This was the first time that German tribes had been covetous of Roman territory in order to settle there themselves. Furthermore, the frontier peoples were now under pressure from the other side. In the depths of the north, there were convulsive movements of population, and huge groups of tribes that had lived round the Baltic were on the trek towards the lower Danube frontiers where Sarmatians and free Dacians now dwelt.
When the storm first broke in c.AD 166, the initiative was taken by the Marcomanni of Bohemia (Czechoslovakia), who traded more extensively with the world of Rome than any of their compatriots, and were also more influenced by its social structure. In the protruding reentrant between Danube and Tisza (now part of Hungary and Yugoslavia) which did not belong to Rome, a branch of the Sarmatians likewise moved to the attack.32 This was a collusive general threat, and it was not unexpected; the onslaught had long been staved off by local Roman officials. But because of major fighting in the east the response of Rome was delayed for too long (p. 22).
The fighting in Marcus Aurelius’ reign was more serious than anything of the kind that had occurred before, and it continued, under the emperor’s personal direction, for most of the remaining fourteen years of his life. The chronology of the campaigns is obscure, but they included two disasters which, according to one interpretation, both took place in the single year AD 170. In the first place, the Germans broke through into the upper Danubian provinces (Rhaetia, Noricum) and into the middle Danube area where flat land on the Roman side presented favourable ground for attackers. Crossing the Alps into Italy, they burnt the town of Opitergium (N.E. of Venice) and laid siege to Aquileia. Secondly, and perhaps almost simultaneously, a German tribe from the Carpathian region surged across the lower Danube and penetrated most of the Balkan peninsula very nearly as far as Athens, for they even plundered Eleusis.33 Marcus’ armies, incapacitated by plague brought back from the east, gradually and painfully regained control, in a long series of campaigns which created an almost desperate financial emergency.
Marcus now had two principal ideas for dealing with the situation. One was to admit large numbers of Germans into the empire as settlers. This would mean that pressure on the frontiers was diminished. The immigrants would also be able to cultivate land which, owing to the inadequacy of its own agricultural populations, was going to waste. And they would be available for recruitment into the army. This importation of northern tribesmen into the empire was not a new concept; Augustus may likewise have pacified a disturbed frontier by admitting 50,000 barbarians, and Nero seems to have settled twice that number. But from the time of Marcus the process became more systematic. The settlers, under special supervisory officials, ranked for many purposes as free men, but they were assigned to Roman proprietors or the leaseholders of imperial domains, and legally tied to their plots of land. The emperors who initiated arrangements of such kinds have been accused of barbarising the empire. But these resettlements broke down racialism, and provided cultivators and soldiers whom the later empire needed in order to survive.
Marcus’ other solution involved annexation. He intended to occupy the Danube–Tisza re-entrant and neighbouring territories and convert them into a new province of Sarmatia, thus shortening and strengthening the frontier, which would then rest upon the long line of the Carpathians. He also proposed to annex Bohemia, together with parts of Moravia and Slovakia, as a second new province called Marcomannia. This would have replaced a long section of the river boundary by the more defensible Sudeten mountains, in continuation of the Carpathian line. Such a move would also have prepared the way for additional future annexations making the total length of the frontier shorter still. With the same idea in mind, Augustus too had wanted to conquer Bohemia, as part of a plan to replace the Rhine-Danube frontier by a less elongated Elbe-Danube line which would have brought the most dangerous of the Germans into the empire.
Augustus had failed, and so did Marcus. His first endeavour to carry out the plan had to be postponed because of rebellion in the east (175),34 and a second attempt was cut short by his death. Perhaps advised by the Bithynian Saoterus to whom these regions must have seemed alien and unattractive, Marcus’ young son and successor Commodus, subject to various agreed conditions for peaceful German behaviour, abandoned the whole scheme. Pursuance of his father’s policy might have transformed the entire future of central Europe by giving the empire more defensible frontiers and many able German cultivators and defenders; and Marcus showed his Romanising intentions when he refused to allow a large group, on whose land he had designs, to emigrate northwards into territories beyond his reach (179).35 On the other hand the conquests would have enormously increased the imperial burden of organisation, development and defence. And so Commodus and his counsellors decided that annexation was impracticable. This decision was deplored by writers who hated the new emperor and liked aggression, but further annexations might well have brought more problems than they would have solved, and the expense was more than the imperial resources, already stretched to the uttermost, could afford.
However, conditions on the northern frontier remained unsettled, and during the next decades there was pressure from the free Dacians living beyond the lower Danube, who had been disturbed by Marcus’ displacements of German tribes.36
Then, under Caracalla, a particularly serious danger came from the more westerly region of the Agri Decumates, in which upper Danube and upper Rhine are close to one another. Here, again as a result of Marcus’ wars, various tribes and portions of tribes had coalesced into a new sort of formidably close-knit federation known as the Alamanni (Alle Männer), who have given their name to the French word for Germany today. After migrating westwards from Brandenburg under pressure from tribes in the heart of Europe, they now threatened the upper Danube-upper Rhine re-entrant. Caracalla, favouring the methods of treachery and encouraging trouble between one German tribe and another, defeated them on the river Main. Yet he also set a new fashion by liking the Germans. He wore their clothes (Caracalla, his nickname, means a German or Celtic cloak), and his murder was attributed, rightly or wrongly, to his preference for the German soldiers who were now playing an important part in the imperial armies.
Caracalla also conveyed extensive subsidies, in gold coin, to the German tribes across the frontiers. This policy, although it may well have been cheaper than fighting, was much criticised, and this criticism had its dangers. For when the young Severus Alexander, after weakening the frontier garrisons to provide reinforcements for the east, proceeded to Moguntiacum (Mainz) and tried to buy off German aggressors, his penalty for not striking a warlike figure was death at the hands of his own troops (238). His successor Maximinus 1, himself a Thracian popular in certain circles beyond the frontiers, re-established peace along the Rhine and upper Danube. But his subsequent expeditions farther east, against the Sarmatians and Dacians, were immobilised by the civil wars that ended in his assassination (238).
The situation in this area, already productive of anxiety, now sharply deteriorated owing to the appearance of new German peoples more formidable than any that had been seen before. The dwellers beyond the lower Danube frontier had for some time been under increasing pressure from remoter areas beyond. For groups of tribes that lived round the Baltic had gradually been journeying towards the Danubian areas inhabited by Sarmatians and free Dacians; and so came the Goths. The long southward treks of this easternmost of the Teutonic peoples was to be celebrated throughout the ages in Germanic national sagas. During their migrations from Scandinavia in about the first century BC they had reached the lower reaches of the river Vistula, and at some date after c.AD 100they started moving south-west.37 Now, under pressure from Sarmatians in their rear, they were establishing themselves not far from the mouth of the Danube. During their travels and settlements in the Black Sea region they had acquired some Greco-Sarmatian culture and political cohesion, which they gradually transmitted to other Germans. Moreover, the Goths, though weak in tactics and siegecraft, were receptive to many Roman military techniques.38
In the 230s they began to burst across the lower Danubian frontier. Their first incursions may have occurred during the reign of Severus Alexander. At all events they crossed the river in 238, and were granted a subsidy by Rome. However, under Philip this was not or could not be paid any longer, and the angry Goths, tempted by Roman civil dissension and usurpation,39 crossed the river again and surged forward as far as the key city of Marcianopolis (Provadiya, west of Varna), which barely managed to hold out against them (248). Philip’s general Decius quelled invasions and mutinies with sufficient success to induce his troops to declare him emperor. But Decius’ reconstruction of the Danube defences proved inadequate, for in Kniva the Goths had a leader of unprecedented calibre, whose large-scale strategy created the gravest perils the empire had yet undergone. Philippopolis (Plovdiv), far inside the empire, was captured by the Goths, and its population exterminated. Then, at Abrittus in the Dobrogea, the emperor himself fell to Kniva, probably with the aid of treachery from Gallus who became his successor (251).
And so in the north, as in the east, an enemy had appeared whose threat to the empire reduced all previous frontier activity, in retrospect, to something scarcely serious. These two menacing hostile forces on either flank took advantage of each other’s activities; so that Rome was faced, for an indefinite period, with the gigantic expense and peril of a war on two fronts. For a time, this proved beyond any emperor’s powers; and catastrophes on the Persian frontiers were matched by simultaneous unprecedented disasters at the hands of the Germans. They came in greater numbers, and at more numerous points, and with better organisation, than ever before, and for a time they could not be withstood. While plague and internal strife raged in the empire, and the Persians overran the orient, the Goths, now joined by another east German people the Burgundians, plundered not only the Balkans but Asia Minor, as far south as Ephesus and as far east as the central plateau (253). Moreover the Goths, obtaining ships from the Greek cities on the Black Sea, embarked successfully on naval incursions which devastated important centres of civilisation such as Chalcedon (Kadiköy). Moreover, ranging much farther afield, they even sacked Trapezus (Trabzon) on the Black Sea and Panticapaeum (Kerch) in the Crimea, with disastrous effects on future Roman agricultural supplies.40
Other northern tribes joined in the onslaught along the whole length of the frontier. Among them were the Franks, a formidable confederacy welded together from various small groups which population movements round the lower Elbe had propelled forward against the Rhine barrier. Repeatedly attacking in compact units of about 30,000 men each, Franks broke through the Roman defences and overran Gaul and Spain, destroying Tarraco (Tarragona) and raiding as far as the north African coast.
Since one man could not face both ways at once, the imperial armies were now divided between two commands, anticipating the later divisions between eastern and western empires.41 Valerian assumed command against the Persians and his son Gallienus took charge of the west and north. Valerian perished, but Gallienus lived and fought on. Nevertheless, the pressure of invasions and the consequent breakaway of the western provinces under Postumus (p. 16) caused the frontier-line, at one important point, to be overrun by the Germans and evacuated by Rome. This was in the region of the Agri Decumates, linking upper Rhine and upper Danube. The abandoned area was never recovered, and the Rhine was henceforward the frontier from its mouth right down to Lake Constance (c.259–60).42 Although neither Gallienus nor Postumus were able to recapture this prong of potentially hostile territory, Postumus succeeded in keeping the Franks and Alamanni out of the rest of Gaul. Gallienus displayed more imaginative ideas. He appears to have authorised the Marcomanni of Bohemia to form a state, or part of one, on the Roman side of the frontier; and he even contracted some sort of a secondary marriage with the daughter of their chief (c. 260).
But soon Gallienus, now sole emperor, was faced with equally perilous German threats farther to the east. Utilising the Heruli, recent arrivals in the Black Sea area, as their sailors, the Goths mustered unparalleled numbers of warriors and ships at the mouth of the Dniester (268). Greece and Asia Minor alike were yet again devastated. The course of events is obscure, largely because writers who disliked Gallienus preferred that credit should instead go to his successor. But it seems to have been Gallienus whom the invaders encountered as they were seeking to return home by the Balkan land-route; he cut off their retreat and won the bloodiest battle of the third century at Naissus (Niš), killing 50,000 of the enemy.43 Thereupon the emperor reverted to the less traditional form of treatment, with which he had been experimenting earlier, by awarding the insignia of a Roman consul to the Herulian prince who had surrendered. But treachery behind the lines prevented the exploitation of Gallienus’ victory, for he was stabbed to death by his own officers.
Yet a start had been made with the extraordinary effort by Rome which, against all likelihood, subjected the Germans to a series of overwhelming set-backs. When the Alamanni struck into Italy itself, Claudius II (268–70) crushed them at Lake Benacus (Garda), and then defeated the Goths in further engagements important enough to earn him the name of Gothicus.44 Their expulsion from the empire was completed by Aurelian. Nevertheless other Germans were still pouring through the Brenner Pass into Italy. But they too, after winning an initial victory, were overwhelmed by Aurelian in two battles fought at Fanum Fortunae (Fano) and near Ticinum (Pavia) (271); and prisoners of war and their families were distributed among the owners of abandoned vineyards in Etruria. Farther east, however, Aurelian decided that the heavily infiltrated trans-Danubian province of Dacia was untenable, and he evacuated the whole region permanently (c. 271), thus shortening and strengthening the frontier.45
A few years later Probus had to meet a huge three-fold German invasion of Gaul (276–7). After dealing with it in spectacular fashion, he moved farther east to confront the Vandals, troublesome German settlers in eastern Hungary who had now invaded the Balkans. Probus revived on a massive scale the policy of settling northern barbarians on Roman territory. And yet, in spite of these concessions, and although the land-hunger of others was relieved by the Agri Decumates and Dacia which Rome had abandoned, the attacks of the Germans did not slacken for long. Tacitus (275–6) was faced with a new invasion of Asia Minor, and Maximian twice had to push back onslaughts upon Gaul. He crossed the Rhine, and, after victories won by his lieutenant Constantius I, was able to advance to the North Sea; a Frankish king was established as a bulwark between Rome and Germany (288). In the following decade Galerius was equally successful against both Marcomanni and Sarmatians, and then Constantine had to deal with Franks and Alamanni (306, 328). At the eastern end of the frontier, too, he built a stone wall from Cernavoda on the Danube to Tomis (Costanta) on the Black Sea (replacing the former earth wall), and with the help of these fortifications the Goths, who had now become prominent again, were heavily defeated (334).
Constantine freely enrolled and promoted Germans, who henceforward provided most of his soldiers and generals (p. 41)-in this sense the German frontier menace had exercised a regenerative effect on Rome. He also continued the policy of importing tribesmen into the empire to farm depopulated areas. He won peace for a generation, but after 350, profiting by attempts of Roman civil war contestants to enlist their help, the Franks and Alamanni won permanent footholds on the Roman bank of the Rhine. Then the shattering defeat of Valens by the Goths (Visigoths) at Hadrianopolis (Edirne) irremediably threw open the Balkan provinces to their settlers.46 From now on more and more German states in treaty relations with Rome established themselves within the frontiers. Indeed these barriers themselves rapidly became obliterated, and by the time Alaric the Visigoth, turning aside from the less vulnerable eastern empire, put Rome to the sack (410), the line had almost ceased to exist. The German tribes were already beginning to form Europe’s kingdoms of the future.
And yet, with only minor withdrawals, those frontiers had been astonishingly held for over a hundred and fifty years after the first terrible Gothic invasions and the destruction, chaos and defeat that they brought; and so the conditions were created by which the classical heritage, instead of collapsing in anarchy, could be conserved and handed on. Rather than enquiring why the Roman empire fell, commented Gibbon, we should feel surprised that it had endured so long. For example, in the continuous peril of the 250s and 260s, amid simultaneous catastrophes from uniquely powerful enemies upon two fronts, there seemed no probability that the world of Rome would survive. Yet it weathered the storm. The turning-point appears to have come in the last year of Gallienus, and then three Illyrian emperors, all commanders of genius, brought about a gradual process of recovery. This was the climax of Roman arms and stamina, and one of the outstanding military achievements of all time. Accordingly Gibbon’s second observation, contrasting the fierce giants of the north with the pygmies who now peopled the Roman world, was wide of the mark. For the army leaders and soldiers of Rome, men of many races, confronted with problems far greater than those that had ever faced their predecessors, saved andprolonged the life of their empire with a vigour that was nearly superhuman.
Yet the price paid for so unlikely a reversal of fortune comprised incalculable losses of life and property and happiness, and the continual expenditure of vast sums of money. The money was needed because, to deal with these mighty problems, the army had to be reorganised and raised to dimensions which previous generations, living in less exacting times, had never conceived of as possible.