The Roman Empire’s increasing reliance on foederati, or barbarian mercenaries, for defense towards the end of its existence was a shift in military strategy that had profound implications for the empire’s structure, stability, and ultimately, its fall.
Origins of the Foederati System
The recruitment of barbarians into Roman military forces was a long-standing practice dating back to the Roman Republic. Julius Caesar and Mark Antony enlisted defeated Gallic and Germanic cavalry for their campaigns. This practice was formalized by Augustus, the first emperor, who established the auxiliary units, integrating conquered barbarians into the Roman army structure. There is no evidence that former barbarian troops or commanders were any less loyal than their Roman counterparts.
The Laeti, like their predecessors in the auxiliary units, were placed on a trajectory of Romanization. This process involved adopting Roman customs, values, and military discipline, gradually assimilating these foreign recruits into the broader Roman society and military culture.
However, by the 4th century CE when the Roman Empire began to face mounting pressures both internally and externally, the proportion of federatii within the Roman army began to rise significantly. The empire had been grappling with chronic manpower shortages, particularly in its military ranks, due to a combination of factors including population decline, economic instability, and the aftermath of the Crisis of the Third Century. Another change in the 4th century was non-Romans were increasingly serving within their own distinct military units, rather than being simply part of the general pool of army recruits
In the context of the Late Roman Empire, laeti were barbarian groups settled within the empire, primarily for military service, while foederati were allied tribes or groups outside the empire who entered into treaties with Rome, also providing military support.
In 358 AD, a significant precedent was set when the entire Salian Franks people were adopted into the Empire. This move provided Rome with a ready pool of recruits. In exchange for being allowed to settle as foederatii in northern Gallia near the Rhine, the Franks were expected to defend the Empire’s borders in their territory and provide troops to serve in Roman units.
The Gothic Precedent
A pivotal moment in the development of the foederati system came in 376 AD when a large group of Goths sought permission from Emperor Valens to settle on the southern bank of the Danube River. The Goths were accepted into the empire as foederati, but this arrangement quickly soured. Later that same year, the Goths rebelled and inflicted a devastating defeat on the Romans at the Battle of Adrianople.
This defeat had far-reaching consequences. The significant losses suffered by the Roman military ironically forced the Empire to rely even more heavily on foederati troops to supplement its forces. In 382 AD, the practice was radically extended when federated troops were enlisted en masse as allied contingents of laeti and foederatii, separate from existing Roman units.
Expansion of the Foederati System
The foederati system expanded rapidly in the late 4th and early 5th centuries. Various barbarian groups, including the Goths, Vandals, Franks, Alans, and even the Huns, fought for Rome as foederati at different times. These arrangements were typically formalized through treaties (foedera), with the barbarian groups receiving various benefits in return for their military service.
The benefits provided to foederati varied but often included:
- Land grants: Foederati were frequently given permission to settle on Roman territory.
- Subsidies: These could take the form of food or monetary payments.
- Autonomy: Tribes were often allowed to fight under their own leaders and maintain some degree of self-governance.
Motivations and Initial Advantages
From the Roman perspective, the foederati system initially appeared to offer several advantages:
- Cost-effectiveness: Foreign troops often required less pay than their Roman counterparts.
- Flexibility: Mercenaries weren’t permanent soldiers on the state payroll, allowing the Empire to compensate them only as needed.
- Expendability: If these hired fighters perished, it could be seen as eliminating a potential future adversary.
- Manpower solution: The system provided a ready source of troops without depleting the Roman citizen population.
For the barbarian groups, becoming foederati offered opportunities for security, land, and wealth, especially as they faced pressures from other groups, such as the Huns, who were ving into their own homelands.
Growing Dependence and Its Consequences
As the 5th century progressed, the Roman Empire’s reliance on foederati troops increased dramatically. This growing dependence had several significant consequences:
Weakening of Native Roman Forces
The initial allure of outsourcing military obligations led to a disinvestment in Rome’s native forces. With fewer troops to train and maintain, funds that would have supported the Roman military were redirected towards paying foederati and other allies. Consequently, while Rome’s ability to muster its own armies never completely vanished, it certainly weakened over time.
The heavy reliance on mercenaries made Rome particularly vulnerable if these hired soldiers decided to rebel. The infamous march of Alaric across Italy is a prime example; during this period, Rome lacked the means to quickly mobilize troops to counter such threats.
Economic Strain
The foederati system, while initially seen as cost-effective, ultimately placed a significant economic burden on the empire. The need to provide land, subsidies, and other benefits to foederati groups strained the empire’s resources, particularly as tax revenues dwindled in the 4th and 5th centuries.
Cultural and Political Shifts
The integration of large numbers of non-Roman troops and settlers began to alter the cultural and political landscape of the empire. The foederati pact served not only a direct military-defensive purpose but also brought many barbarian tribes within the cultural and political orbit of Rome.
The Visigoths
The Visigoths provide a prime example of the complex and often tumultuous relationship between Rome and its foederati. Initially accepted into the empire in 376 AD, they rebelled two years later, inflicting a devastating defeat on the Romans at Adrianople. Despite this, the Visigoths were again brought into the foederati system in the early 5th century. Under their leader Alaric I, who began his career leading a band of Gothic foederati, they eventually sacked Rome itself in 410 AD.
The Vandals
The Vandals, another Germanic group, also served as foederati before eventually turning against Rome. They crossed into Gaul in 406 AD, breaching the Rhine frontier that had been defended by Frankish foederati. The Vandals then moved into Spain and eventually established a kingdom in North Africa, dealing a severe blow to Roman power in the western Mediterranean.
The Turning Point: Attila and the Battle of the Catalaunian Plains
The Battle of the Catalaunian Plains in 451 AD marked a significant turning point, highlighting both the extent of Rome’s reliance on foederati and the system’s potential strengths and weaknesses. Attila the Hun was defeated only with the help of foederati troops, particularly the Visigoths under King Theodoric I. This battle demonstrated that the foederati could be effective in defending Roman interests, but it also underscored the empire’s inability to field a predominantly Roman army against major threats.
The Final Century of the Western Empire
In the last century of the Western Roman Empire’s existence, its military strength was almost entirely reliant on foederati units. This dependence created a precarious situation where the empire’s fate was increasingly in the hands of semi-autonomous barbarian groups with their own agendas and ambitions.
The revolts led by foederati had dire long-term repercussions. Unlike earlier Roman civil wars, where rival factions often sought to improve the land to gain strategic advantages, foederati rebellions typically involved widespread looting. This left vast areas of the Empire unable to contribute significant tax revenue, creating a vicious cycle where insufficient funds hindered the Empire’s ability to recruit enough soldiers to reclaim lost territories or enhance its military capabilities.
The Eastern Empire’s Approach
The Eastern Roman (Byzantine) Empire also made use of foederati, but generally managed the system more effectively. In the East, the foederati were often more tightly integrated into the imperial military structure. For example, on the Arabian frontier, the Byzantines entered into agreements with Arab tribes to help secure the Limes Arabicus against Persian-allied nomads.
Legacy and Historical Debate
The increasing reliance on foederati was both a symptom and a cause of the Western Empire’s weakening. It reflected the empire’s inability to muster sufficient manpower from its citizen population and its economic struggles. At the same time, it accelerated the process of decentralization and the erosion of direct imperial control over its territories.
What began as a pragmatic solution to manpower shortages and border security ultimately became a critical weakness. The foederati system provided short-term military advantages but led to long-term strategic vulnerabilities.
As the Western Empire weakened, it became increasingly reliant on foederati who were only loosely bound to Roman authority. This reliance accelerated the empire’s fragmentation, as foederati groups carved out their own kingdoms from imperial territory. By the time of the last Western Roman Emperor, Romulus Augustulus, in 476 AD, the empire’s military power rested almost entirely in the hands of barbarian foederati. The story of Rome’s foederati is thus a cautionary tale about the risks of outsourcing core state functions like defense.
The Eastern Empire’s more successful management of foederati relationships was one factor that allowed it to survive and evolve into the medieval Byzantine state, demonstrating that the challenges posed by the foederati system were not insurmountable, but required careful and strategic management.
