The western provinces had been unprotected by Roman troops when a combined force of Vandals, Alans, and Suebi crossed the frozen Rhine in mid-winter 406 (Zosimus 6.3.1; Jerome, ep. 125). This revelation of the vulnerability of the Gallic provinces led inevitably to usurpations. The most serious of these was that of Constantine III, who moved into Gaul from his British base and established himself at Arles. This led to a bewildering series of conflicts which persisted until 414 when the beginnings of a new political order began to take shape. Symbolically a key moment was the marriage in Narbonne of Athaulph, Alaric's successor, to Galla Placidia, Theodosius I's daughter by his first marriage, and half-sister of Honorius. Orosius' history Against the Pagans (a work which had been commissioned by St Augustine to set the fall of Rome into the context of Roman history and demonstrate that it had not occurred due to the neglect and anger of the pagan gods) contains a famous account of this event:
Athaulph was then the king in charge of the Gothic peoples. He had succeeded to the throne after the capture of the city of Rome and the death of Alaric, and had taken as his wife Placidia, the sister of the emperor.…I heard a person from Narbo, of high military rank under Theodosius, a man also of devout, prudent and serious character, relating in Bethlehem, a town of Palestine, to the priest Jerome, that he had been a close friend of Athaulph at Narbo and had often heard him say on oath, that he had first ardently desired to obliterate the Roman name and to render and name the entire territory of the Romans the empire of the Goths, so that, to speak vulgarly, what had been Romania should become Gothia, and that Athaulph should become what Caesar Augustus had once been. But when he had discovered from much experience that the Goths were totally incapable of obeying the rule of law because of their untempered barbarism, and that the laws of the state ought not be defied, since without them a state is no state, he had gradually chosen to seek glory for himself by restoring to its former state and enhancing the Roman reputation through the use of Gothic might, so that he might be considered by posterity as the author of the revival of Rome, after he could not be its transformer. (Orosius 7.43)
The marriage did not last and in the short-term the entente with Athaulph collapsed, but the Romans enlisted the Goths as allies against the Germanic tribes, which had taken control of much of Spain since 409: the Suevi and the Hasding Vandals in the northwest, the Alans in the center, and the Siling Vandals in the south of the Spanish peninsula.25 In 418 Honorius' general Constantius escorted the Visigoths back across the Pyrenees to Aquitania, where they settled in the valley of the Garonne between Toulouse and Bordeaux and established a kingdom that lasted until 507. He also reorganized the provincial council of the so-called seven provinces of Aquitania, part of a wider attempt to bring order to the whole region. Constantius married Galla Placidia on January 1, 417 (Olympiodorus fr. 33). The union produced a daughter, Honoria, and a son, the future emperor Valentinian III, who was born in July 419. In that year Constantius was named consul for the third time, and in 421 he was raised to the rank of Augustus. He was to die suddenly later in the same year but the future of the western Roman dynasty was now mapped out. The outcome of the decade since the fall of Rome had been better than the Romans might have reasonably hoped for. Spain and northern Gaul had slipped from their control, and the defense of Britain had been abandoned (Zosimus 6.5.3, 10), but the regime of Honorius had consolidated its control of Italy, Africa, and southern Gaul. The Goths controlled Aquitania until their defeat by the Franks in 507.26
In the West, the large Germanic incursion that is dated to the last day of 406 may have been a decisive moment in the break-up and eventual collapse of the western empire. Peter Heather has analyzed the long-term consequences in a fine study. The cession of territory to the invaders meant a loss of revenue and power. The local landowning elites of the western provinces began to make compacts with the newcomers or look to their own defense. This promoted the dissolution of the old empire over two or three generations.27 The large number of barbarian groups began to put the western provinces under perceptible pressure from the beginning of this process. Goths, Suevians, Burgundians, Alans, and Vandals all seized or claimed and were conceded land on which to settle, with the result that the empire relinquished a significant part of its revenue from taxable land (Map 4.1). As it became clear that the empire was less able to protect them, local landowners now began to waver in their loyalty to Rome and their readiness to pay taxes. Tax revenues also fell, as areas, including Britain in 410, seceded and looked to their own defense. Moreover, remissions had to be given to war-torn areas, including Italy in 413 (CTh. 11.28.3, 12), and Sicily in 440, and this put an increasing burden on other regions. The issue became acute in 439, when the Vandals took Carthage and cut off the income that the western empire derived from Africa. This provoked an ineffective counter-offensive led by Aspar from Constantinople.
Map 4.1 Map of the western empire showing areas of barbarian settlement in the mid-fifth century (StepMap GmbH)
Honorius died childless in August 423, and a struggle for power led to the brief usurpation of John, a prominent figure of Constantius' court. His reign was cut short by the decision of Theodosius II and his advisors in Constantinople to send forces to install Valentinian III, the 6-year-old son of Constantius and Galla Placidia, as western emperor in October 425. The political uncertainties of this episode saw the emergence of the dominating military figure of the western empire, Flavius Aetius, son of Gaudentius. Aetius had spent part of his youth as a hostage among the Huns.28 Acting for the usurper John, he had brought a large Hunnish force to resist the east Roman forces. The Huns arrived too late to save John, but their intervention brought its own problems, as Aetius' men clashed outside Ravenna with a force sent by Theodosius II, and blood was shed, before Galla Placidia produced money enough to buy off the Huns and send them back to the middle Danube regions (Philostorgius 12.14). Aetius negotiated a senior military command for himself in Gaul under Valentinian III as his price for persuading the Huns to return home.
In 430 Aetius had to call on his Hunnish connections again to consolidate himself against challenges from Bonifatius and Sebastianus, who held high commands in Africa and were rivals within the western military hierarchy. But from 433 he retained the position of magister utriusque militiae until his death twenty-one years later. During this period he succeeded in maintaining the stability of Gaul and protecting the interests of its Roman landowners, despite the collapse of the old frontiers. Aetius made no attempt to prevent the growth of Hunnic power in the Danubian regions, and indeed depended on the support of the Huns to maintain his own position. This period saw Illyricum fall under the domination of Attila, whose threats to the empire were only checked by a continuous flow of tribute payments from Constantinople (see pp. 215–6). In 451 Attila, by choosing to lead an expedition against the West, relieved the pressure on the eastern empire. This enabled Marcian to reverse Theodosius II's policy and withhold tribute payments. Attila now pursued western ambitions, encouraged by Valentinian III's sister Honoria, who offered herself to him in marriage to avoid alternative arrangements made by the emperor. Attila took his forces into Gaul, to claim his share of the western empire, but was checked at the battle of the Catalaunian Plain, by a coalition of Aquitanian Visigoths under Theoderic and Roman troops under Aetius. The next year the Huns invaded Italy and plundered Aquileia, Milan, and Ticinum, but a famous parley between Attila and Pope Leo spared the city of Rome. A year later Attila was found dead, choked by a nosebleed after wedding-night excesses with a Gothic princess.29 In 454 Valentinian III assassinated Aetius with his own hands, but was himself killed a year later by two of Aetius' followers.
In 411 the Germanic peoples who had crossed the Pyrenees had used lots to divide the Spanish peninsula.30 The Suebi in the northwest corner of the peninsula were set upon by the Vandals, but saved by Roman forces. The Siling Vandals moved to the south. After capturing Hispalis and the port of Cartagena in Baetica in 428, they crossed the Strait of Gibraltar in the following year, with their eyes on richer pickings in Africa. The wealthy cities and fertile lands of Africa had been a target of barbarian ambitions previously, both for Alaric in 411, when he reached Sicily after the sack of Rome, and for the Visigoths under Athaulph in 414. Africa and its capital Carthage represented a larger prize than anywhere that had fallen to the barbarians except for Rome itself. The Vandal ruler Gaiseric organized his followers into eighty contingents each of a thousand persons (including non-combatants) for the sea passage. The figure suggests that the Vandals' fighting strength was around 20,000.31 They had already operated over many years in Spain, and their ability to organize the sea passage for such a large group implies a growing level of social organization and collective discipline. This was certainly consolidated during their prolonged but systematic expansion westwards across the African provinces, which only achieved its final goal, the capture of Carthage, in 439. It was during this long march that the identity of the Vandal kingdom was forged.32 The case of Hippo, St Augustine's bishopric, which withstood a Vandal siege for more than a year before it fell in July 431, shows the strength of local opposition. A first stage of the Vandal incursion continued until 435, when a treaty with the Romans ceded them Mauretania and western Numidia.33 The offensive was resumed against the eastern provinces of Africa Proconsularis and Byzacena, which were covered with small cities.
Carthage, the capital and one of the great cities of the Mediterranean, fell in 439. The Vandals thus gained greater leverage over the western Roman Empire than any other barbarian group. They became an immediate threat to Rome and Italy, and may only have been deterred from invasion by the naval expedition of 441 which was dispatched to the western Mediterranean by Theodosius II. In 442 the Vandal conquest of Africa was acknowledged in a new treaty agreed with the western emperor, which reversed the terms of 435. Wealthy Proconsularis and Byzacena were now Vandal territory, while Numidia and Mauretania reverted to Roman control. The agreement with Rome was placed on a firmer footing than before.34