Chapter 4 - A Transition of War
Throughout the first and second centuries, the Roman strategy succeeded in repelling the repeated attempts at penetration by the Germans. It was not until 260 A.D. that the first significant penetrations succeeded when the Franks moved into Spain, the Alamanni moved into the Alvergne country, and the Goths crossed the Danube in large numbers. The Roman army, long garrisoned along the imperial frontiers, had begun to decay. Many of the frontier posts had become large towns with large civilian contingents within them. Training and discipline declined. By the second century not more than one percent of the Roman army was comprised of native Italians, the rest being drawn from other nationalities of the empire still strongly socialized to Roman values and methods. By the middle of the third century, however, the army had become hollow, and the German tribes broke through in great numbers to settle large tracts of imperial land.
The Roman response was to reorganize the army with militia troops, the limitani, garrison the forts, and hold strong horse-born reserves at key garrisons within the empire that could rush to a point of penetration and stop the enemy advance. Most of the army by this time was comprised of barbarian soldiers in the pay of Rome. As Roman reliance upon these barbarian military forces grew, the organizational structure and values of the legion began to erode until, by the 4th century, the legions were no longer organized along traditional Roman lines. Instead, they reflected barbarian weapons, tactics, values, and were commanded by their own tribal chiefs. The fiction that they were paid allies of Rome continued until the 5th century when renewed waves of barbarian invasions crashed over Europe, effectively putting an end to the Roman military system.
The gradual barbarization of the legions had an enormous impact on Roman military organization. The decline in the administrative and support structure of the legion led to its replacement with a number of barbarian military practices. In effect, the tribal military forces within the empire became a state within a state that was beyond the power of the central Roman state apparatus to control. The Battle of Adrianople administered a military coup de grace to a social order that was already dying from within.