Barbarian Invasion: The Beginning of the End for Rome?

According to the account of Prosper of Aquitaine, a contemporary Christian writer whose life was thrown into disarray by Gothic incursions into the Roman Empire, a large-scale crossing of the Rhine by barbarian confederations occurred on 31st December 406. This migration was a crucial moment in the decline of the Roman Empire in the west and marked the beginning of a tumultuous period which saw widespread raiding and the collapse of Roman order in the provinces. The crossing, or ‘barbarian invasion’ of 406 led to a breakdown of central Roman power along the Rhine frontiers and arguably instigated the usurpation of Constantine III, a rebellion that presented a grave threat to the Western Emperor Honorius. 

The crossing of the Rhine in 406 AD was part of a period of European history known as the Migration Period,’ or the ‘Barbarian Invasions.’ Lasting from the mid-to-late-4th century until the 560s, large numbers of Germanic peoples, Huns, Avars, and Slavs either migrated within the Roman Empire’s boundaries or else migrated into the Empire from outside its borders. Traditionally, the arrival of the Huns in Europe in 375 is considered the beginning of the Migration Period, while the Lombard conquest of Italy in 568 marks its end.

There is a great deal of debate concerning the cause of these migrations. Were these opportunistic tribal warbands intent on looting and pillaging Roman cities, or were they refugees fleeing from more powerful political entities further east, such as the Huns? The construction of the Great Wall of China has been suggested as a cause for the migrations, forcing tribes westward, creating a domino effect that led to Germanic tribes moving into the Western Roman Empire. Climate change, poor harvests, and population pressures have all been cited as reasons for these large-scale movements.

The discussion also revolves around the relationship between these migrations and the collapse of the Western Roman Empire: namely, did the empire collapse as a result of these ‘barbarian invasions,’ or did the slow decline of the empire which had been cemented by the ‘Crisis of the Third Century’ initiate a period of (often violent) migration?

Certainly, the sudden appearance of thousands of barbarians in the empire, and the warfare that occurred as a result, would suggest the former. However, archaeologists have suggested that many of the ‘barbarians’ who crossed into the Roman Empire already lived in established agricultural communities and were actually drawn into Roman political disputes which led to their steady resettlement within the empire itself. It seems likely that these were not desperate peoples venturing across the frontier out of necessity.

In fact, across many of their borders, the Romans had long maintained relationships with barbarian groups living on or beyond the frontier. Through the giving of gifts and conferment of imperial legitimacy, the Romans were able to build alliances with friendly barbarian chieftains, who in turn acted as buffers against potentially hostile barbarian groups beyond. The breakdown of central authority and the fragmentation of power in the late Western Roman Empire meant these relations were neglected, even to the point of former border allies moving into Roman territory, and assuming control of the local area. 

In many cases, this happened with the support of the local Roman population. If the central government in Rome was not able to send troops to maintain order and political control, why not allow a local chieftain, possessing the military might to protect the region, to take charge? It is likely in this way that the Western Roman Empire steadily broke down and was replaced by emerging barbarian kingdoms.

It is the contemporary author, Prosper of Aquitaine, who gives us the precise date for 31st December 406 for the crossing of the Rhine. Although it is unknown exactly how the river would have been crossed, a suggestion by the 18th-century historian Edward Gibbon that the Rhine was frozen has become popular – of course, it is also highly possible that the barbarians used boats or an existing Roman bridge.

It is unknown how many people crossed, or what they would have looked like, although it seems likely that they would have been organized in tribal societies formed through the process of ‘ethnogenesis’ – the formation of an ethnic group, perhaps with a shared language. 

We do have a list of the peoples who crossed from contemporary authors, but the accuracy of these lists is all but impossible to ratify. Jerome, writing in 409, informs us that the migration involved Quadi, Vandals, Sarmatians, Alans, Gepids, Herules, Saxons, Burgundians, Alemanni, and Pannonians. It is important to note that some of these groups were strongly associated with literary and historical tradition at the time and were likely to have been synonymous with barbarians in general.

According to the fragments of a lost account by the contemporary historian Renatus Profuturus Frigeridus (known as the ‘Frigeridus fragment’), there was a tribal group of Frankish foederati, allied to the Romans, who resisted the Rhine crossing. The Franks were winning a war against the Alans under King Godigisel, until support from a group of Alans turned the tide late in 406, paving the way for a large-scale crossing of the frontier during the winter.

Following their crossing of the river, it is unclear whether the groups involved in the barbarian invasion moved together as a tribal confederation or diverged and separated. What is clear is that a wave of violence ensued, and several Roman cities in the region were sacked, including Mainz, Worms, and Strasbourg. This upheaval in northern Gaul continued until at least 409. It met little to no resistance from the Western Roman Emperor Honorius, who had only just managed to repulse an invasion of Italy by the Gothic King Radagaisus, and who was preoccupied with political machinations in Rome.

So why did these tribal groups cross the Rhine at the end of the year 406? The fact that the border was relatively lightly defended, or almost totally unguarded, could have been one of the primary reasons. It has been suggested that the Roman general Stilicho greatly weakened the Rhine’s defenses in 402, withdrawing troops to deal with Alaric I’s Visigothic invasion of Italy, and leaving the border defenses in the hands of Frankish and Alemanni allies. This, combined with the weakness of Honorius’ government in Rome, made crossing the Rhine and looting the cities beyond it a tempting proposition.

It has also been posited that the group who crossed may have been the remains of Radagaisus’ failed invasion of Italy earlier in 406, or groups of barbarians who had been pushed westwards, fleeing the encroaching Huns. Historian Peter Heather has argued that the evidence for widespread withdrawal of Roman troops from the Rhine in the years before 406 is weak and that therefore those who crossed the Rhine were more likely to have been refugees than opportunistic raiders. The fact that they moved in the middle of winter, arguably the worst time of the year for military campaigning, supports this idea.

Dating Issues

It is worth noting that the dating of the Rhine crossing has been disputed, specifically by historian Michael Kulikowski. In a 2000 article, he suggested that 31st December 405 was in fact a more likely date, citing the possibility that Prosper was spacing major events in his chronicle so as to have one occurring in each calendar year. 

A December 405 dating also explains why the Roman general Stilicho did not act against the Rhine invaders, as he would have been busy fighting Radagaisus forces – if we accept the traditional date of December 406, Stilicho’s inaction is notable and difficult to explain. Furthermore, the contemporary historian Olympiodorus of Thebes asserted that the Rhine barbarian invasion caused the usurpation of Marcus in Britannia in mid-406, another discrepancy which an earlier 405 dating of the crossing would solve. 

Whether it occurred in December 405 or 406, the consequences of the Rhine crossing were dire for the Western Roman Empire. This group of tribes of the barbarian invasion looted several cities across northern Gaul and were able to move essentially unchecked by the Roman authorities – it was only the actions of the usurper Constantine III that seemed to end their violent progress. By 409 they had reportedly reached Hispania. Although there are no reports of widespread looting occurring throughout central and southern Gaul, the presence of these barbarian groups certainly destabilized Roman power and made provincial Romans less dependent on the central government.

In Britain, the revolt of the usurper Marcus, which may have been caused by unease and dissatisfaction at the Rhine crossing, developed into a major issue for the Western Emperor Honorius. When Marcus and his immediate successor Gratian were both killed after falling foul of their troops, general Constantine III rose to command the British legions, who swiftly declared him emperor.

Crossing into Gaul in 407, Constantine won a series of battles against the groups of the barbarian invasion who had breached the Rhine frontier, restoring some semblance of order. By mid-408 he had established his capital at Arles and was minting coins, and by 409 he had defeated Honorius’ allies in Hispania and forced the Western Emperor in Rome to recognize him as co-emperor. Having executed his best general Stilicho for treason, and facing another invasion of Italy by Alaric I, Honorius had little choice but to accept.

Although Constantine’s usurpation soon fell apart through the rebellion of his own generals and military defeat to Honorius’ new general Constantius, the usurper had badly damaged the Western Empire. The barbarian invasions had breached the Rhine frontier, and various barbarian groups had settled in the empire after the crossing of 406. The province of Britannia was lost as well, never to be regained.

Therefore, the Rhine crossing of 406 was a seminal moment in the decline of the Western Roman Empire, as well as exacerbating the rebellion of Constantine III. As a result of the ‘barbarian invasion,’ the empire abandoned one of its long-standing frontiers and was forced to allow various barbarian groups into the political landscape of the empire. It is these barbarian polities that would go on to grow into the kingdoms that would eventually replace the Western Roman Empire.