Summary

The armed forces of the late empire remained of central importance in a world whose geopolitical certainties and assumptions had been severely shaken by the upheavals of the 3rd century. Those upheavals and the changed international landscape which emerged prompted significant reconfigurations of the empire’s armies and their command, as well as an expansion in their size, with far-reaching consequences for governmental infrastructure and economic resources.

The most fundamental organizational change was the separating out of a strategic reserve of elite troops from those forces based in the frontier provinces, with a greater emphasis on mobile cavalry units. During the 4th century, that reserve evolved into a number of regional armies, some of which then fragmented under the impact of further upheavals in the late 4th and 5th centuries, especially in the western half of the empire. However, the armies of the eastern half generally proved more resilient and provided the basis for a period of renewed expansion in the 6th century. Although the armies of the late empire suffered significant defeats and setbacks, they also achieved some notable successes, and the military history of the period should not be characterized solely as one of inexorable and inevitable decline.