Indeed, one of the factors in the morphing of the republic into an empire was the need for a new form of government which could manage this large and growing territory. The republic was a type of government best suited to a city-state which had a modest amount of surrounding land under its rule. A large, multi-continental required a different governmental structure.
Although not as sharply distinguished as in the twenty-first century United States, it can still be said that in the Roman Empire there was some distinction between the civilian government and the military. To be sure, that distinction was at times blurred, as in the case of the civil wars between 49 B.C. and 27 B.C. which led up to the end of the republic and the beginning of the empire.
The Roman military featured private armies which owed their primary allegiance to their commanding generals, and not to the nation or government.
While the military devoted attention to tactics — the different types of weapons and how they were used, various formations of soldiers in combat, etc. — historian Edward Luttwak argues that it was not tactics, but rather strategy, which primarily shaped the Roman armies and which led to their victories and defeats.
Luttwak writes that the successes of the Roman military were achieved, not because of their tactics, but rather despite their tactics:
Had the strength of the Roman Empire derived from a tactical superiority on the battlefield, from superior generalship, or from a more advanced weapons technology, there would be little to explain, though much to describe. But this was not so. Roman tactics were almost invariably sound but not distinctly superior, and the Roman soldier of the imperial period was not noted for his élan. He was not a warrior intent on proving his manhood but a long-service professional pursuing a career; his goal and reward was not a hero’s death but a severance grant upon retirement. Roman weapons, far from being universally more advanced, were frequently inferior to those used by the enemies whom the empire defeated with such great regularity. Nor could the secular survival of the empire have been ensured by a fortunate succession of great feats of generalship: the Roman army had a multitude of competent soldiers and a few famous generals, but its strength derived from method, not from fortuitous talent.
Over time, there were shifts in emphases: At some times, the Romans looked more toward fortifications — walls, watchtowers, fortresses — to solidify the borders; at other times there was less emphasis on such structures, and more emphasis on keeping mobile groups of soldiers ready to move into regions of sudden or unexpected conflict. Likewise, there were variations between times in which the army was composed mainly of Romans, and other times in which many of the soldiers were mercenaries, foreigners, or both.
Changes in the priorities of the civilian government led to changes, Luttwak asserts, in the strategies employed by the military:
Three distinct methods of imperial security can be identified over the period. Each combined diplomacy military forces, road networks, and fortifications to serve a single objective, functioning therefore as a system up to a point, albeit with local variations, interruptions, and exceptions. But each addressed a distinct set of priorities, themselves the reflection of evolving conceptions of empire: hegemonic expansionism for the first system; territorial security for the second; and finally, in diminished circumstances, sheer survival for the imperial power itself. Each system was based on a different combination of diplomacy, direct force, and fixed infrastructure, and each entailed different operational methods, but more fundamentally, each system reflected a different Roman world view and self-image.
This tripartite division of the imperial era can be illustrated with examples. The first, expansive, phase is seen in, e.g., the conquest of Gaul, or the invasion and occupation of the southern half of Great Britain. The second phase, securing the borders, led to the construction of structures like the limes between the Rhine and the Danube, or the construction of Hadrian’s Wall between England and Scotland. The final phase, during the gradual contraction of the empire, included defensive fighting against Germanic tribes, Huns, and Persians.
While the five centuries of imperial military activity make for a rich and complex narrative, Edward Luttwak’s identification of these three stages creates a useful larger framework for understanding both the military history of the Roman Empire, as well as the interrelations between the civilian and military histories.
