For the most part, the old Roman aristocracies in the core regions of the Western Empire survived the tumultuous fifth century and proceeded to adjust to life under the new ‘barbarian’ kingdoms. Aristocratic culture was changing though, and while the Gallo-Roman aristocracy continued to take part in certain elements of traditional Roman aristocratic culture, over time the status markers of the old elite civic culture gave way to changing values and traditions.
Northern Gaul likely experienced a more rapid collapse of Roman aristocratic culture. The northern regions of Gaul had always been more dependent on imperial patronage and office during the late Empire. Following a series of failed usurpations in the closing decades of the fourth century, imperial activity largely withdrew from its territories north of the Loire, moving the Gallic from Trier to Arles. The archaeological record indicates a fairly rapid collapse in villa life and a stagnation of Roman industries. It also appears that some aristocrats moved south, and the Notitia Dignitatum from 418 notes that several Gallic offices had been withdrawn from the North and removed to the South. In the early fifth century the Empire also began to settle federated barbarian groups in Southern Gaul, including the Visigoths in Aquitaine and Septimania. The settlement of these groups so deep in Gallic territory supports the conclusion that the empire had all but withdrawn from northern Gaul and that the effective border was now along the Loire. Until the crises of the second half of the century, the Visigothic presence in the region does not appear to have disrupted the local aristocratic culture. Unlike the north, southern Gaul was not as reliant upon public offices and imperial patronage to convey status; the region was much wealthier than the north, as indicated by the large landed estates still maintained by the aristocracy throughout this period.
The barbarians, however, did fill a niche left by the slowly waning imperial administration. The new rulers functioned as source of patronage that local aristocrats could access in order to advance social status and retain power on a local level. The situation is similar in the north, though to a much greater degree, due in part to their aforementioned dependence on imperial patronage. Roman society in southern Gaul simply did not experience the same level of social disruption in the first half of the fifth century. Of course, it was not simply a matter of exchanging the Empire for a barbarian patron. In the north, the Franks and Alamans along with local Roman military leaders had stepped in to fill the political vacuum left by the Empire and quickly became the foci of local politics. In the south, particularly in the latter half of the fifth century, the relationship between the Gallo-Roman aristocracy and the Visigoths could get messy. In the 470s, the Visigothic king Euric annexed large swathes of southern Gaul, something that did not sit well with the local aristocracy, and many raised their own forces (NOT imperial forces) to challenge the Visigothic king. The reality is, the Gallo-Roman aristocrats were political agents in their own right throughout this period, and frequently mobilized their own resources for and against the Goths. Now what does all this mean for Roman aristocratic culture in Gaul? Generally speaking, there is more of a social and cultural continuity of the senatorial aristocracy in central and southern Gaul. Traditional aristocratic activities, or at least attempts at them, continued. Letter writing especially is an important example, as letter caches, particularly those penned by Sidonius Apollinaris, are among some of our best sources for the period.
However, that does not mean that aristocratic culture was not changing. Civilian aristocracies in general became more militarized and, with the exception of a career in the Church, became the main business of elites over the course of the early medieval period. Arguably, the formation of a landed and militarized aristocracy is a solid indicator that we are leaving the world of late antiquity and are entering something more recognizably medieval. The markers of the old civic culture of the Roman aristocracy were gradually becoming less relevant, replaced with other values and emphases. As can be guessed, the breakdown of the old social order occurred much more rapidly in Northern Gaul than elsewhere in the Gallic provinces.
It is difficult though, to discern whether or not such changes are the result of ‘Germanic’ influence. The so-called barbarian law codes have strong Roman antecedents and were likely compiled with the aid of individuals familiar with Roman jurisprudence. An emphasis on aristocratic meat-eating and the public assembly of all free men –reflecting direct ties to the king—do appear to be important Germanic contributions. The truth is, it is really quite difficult to distinguish Roman and Barbarian, as both are fluid identities. And it only gets more difficult as time wears on. While Roman aristocracies remained in place throughout the post-Roman world, what it meant to be Roman was changing and gradually disappearing in the wake of social, political, and economic trends. By the mid seventh century, people in the barbarian kingdoms of Western Europe had ceased to identify as Roman; they were instead Visigoths, Lombards, Franks, and Burgundians. While tied in part to the barbarians who had entered the Empire in the fifth century, the ethnogenesis of these groups reflects the increased localization of politics and economy, and to the extent to which regional aristocracies were realigning along new networks of power and patronage. Marginalized northern Gaul rapidly adopted a new Frankish identity and had more or less done so by the close of the sixth century. As expected, old Roman ties held out longer in the south, even as the region fell under Frankish rule. However Aquitaine, isolated from the core area of Gallic politics in the north, never really went for a Frankish orientation, aligning more with the Basques and something of a Gascon identity.
So the aristocracy never disappeared. Values and identities changed over time, but for the most part those who had wealth and land persisted, such that some elites well into the sixth and even seventh centuries bragged of their senatorial lineages.
The above is a very broad overview of a very complex topic. I suppose something could also have been said for the Kingdom of Soissons, a Roman holdout in the North, but I know little about the subject (to be fair, I am not sure there is much to say other than that it also is a product of an increasingly militarized and changing political landscape). If you have any follow up questions, please feel free to ask!
Readings-Sources:
Halsall, Guy “The Barbarian Invasions” in The New Cambridge Medieval History. Vol 1, Ch 2. 2005.
Wickham, Chris The Inheritance of Rome. 2009
Wood, Ian The Merovingian Kingdoms: 450-751. 1994