The history of Rome is, in many ways, the history of the frontier – how it expanded and was governed and secured. Edward Luttwak, a professor of strategic studies, brings a unique perspective to a topic that has long remained, for better or worse, the realm of classical scholars.
The overarching theme is that the Romans perfected a hegemonic system of control by the late Republic, which was maintained well into the first century of the empire. It rested primarily on deterrence and a network of client kingdoms; its hallmark was an incredible economy of force and flexibility. From the second century to the collapse of the empire in the early fifth century, Roman frontier policy steadily drifted away from the efficiency of deterrence to a direct physical defense of the enormous border. Once this transition was complete, Roman military strength and effective power became rigidly proportional: strength was used directly, rather than as a tool of political suasion.
Luttwak breaks his argument into three broad phases of frontier policy. The first phase, which he terms the Julio-Claudian system of “Client States and Mobile Armies” (from Augustus to Nero, 31BC to 68AD), was marked by a thoughtful and rather nuanced economy of force in a hegemonic empire system. The 28 legions (300,000 men) were distributed on the periphery of the empire and served as a mobile strike force designed to maintain stability and put down internal revolts. A notable feature of the Roman defensive policy of this period, he argues, was a “lack of a perimeter” along the 4,000 mile rim of the empire. There were no fixed borders or defensive positions.
The stability and effectiveness of this system rested on two critical, interrelated concepts: 1) escalation dominance; and 2) armed suasion. Half of the Roman army (roughly 150,000) were auxiliary forces provided by the client states, which were critical to Roman military might, but unable to challenge the 28 legions of heavy infantry in pitched battle. This clear cut military advantage and overwhelming force deterred resistance to Roman rule by client states and border peoples, alike. Thus, the Romans could achieve a tremendous amount of power – diplomatic, economic, social – from the implied threat of military force. So long as potential rivals could perceive Roman power and had tangible assets (cities or lands) that could be laid waste, there was small chance they would resist Roman dominance. “The empire’s potential military power could be converted into actual political control at a high rate of exchange,” the author argues.
Roman power was real, but was most effective only when properly interpreted by client states and tribes without actual use. Thus, the foundation of the security system during this period was a complex network of client state relationships. And the susceptibility of those states or tribes to a land power that presented an existential threat to cities and agriculture. (Luttwak notes that it was the less sophisticated, semi-nomadic Barbarians in the west who would challenge Rome, often effectively so, primarily because they failed to grasp the extent of Roman power and had less to lose than the more civilized and urban cultures of the east.)
The second phase, the Antonine system of “Scientific Frontiers and Preclusive Defense” (from Nero to Marcus Aurelius, 68-180AD), was marked by the emergence of imperial borders that are clearly defined and, to a certain extent, permanently defended. The old client states of the Julio-Claudian system were absorbed into the empire (to maximize tax collection?), while the new border defense (limes) was built on a network of roads connecting the frontiers to garrisons. The purpose of this defensive strategy, Luttwak asserts, was not to defend against all threats, but only against “low intensity” raids – small, mobile bands of barbarians seeking targets of opportunity. The Roman response to genuine strategic threats remained the same as before: offensive, overwhelming, mobile and beyond the border.
Luttwak maintains that the physical barriers of the perimeter defense were just the skeleton of the overall system. The main difference between the Antonine period and the Julio-Claudian was the emergence of the “preclusive” ability to defend against low intensity threats. Both systems could provide ultimate security to the empire, but only the preclusive system could ensure civil security. Luttwak argues that both systems made sense, but only under different strategic goals. By the time of the Flavians, continuous security of civilian life and property was critical, although he never really explains the reasons behind this fundamental change in policy.
In addition to preclusive security, the other term that Luttwak introduces here is “scientific frontiers,” those based on more than tactical or geographic convenience but rather strategic rationale. He postulates that there is a consistent pattern of Roman frontier policy and a hierarchy of priorities. First, frontiers must facilitate strategic transit between continental regions of the empire. Second, it should not include areas difficult to pacify, settle and Romanization (e.g. Scotland). Third, it should include areas of natural resources and large manpower that are culturally open to Romanization. And finally, the frontier should be as short as possible.
The final phase, “Defense in Depth” (the most powerful influence being Diocletian), was noted by a major differences in the pattern of border defense. By the third century, fortifications were situated in tactically strong positions; the new fort lay-out was smaller in perimeter and square in nature (rather than the old rectangular forts with shallow moats); the outer defenses became much bigger and thicker, all to increase the likelihood of sustained resistance. In other words, defensible hard points rather than bases for offensive operations. Once the new strategy was undertaken, it required defenses on a local scale with local efforts. Luttwak really stresses that the major change from the Antonine period to this later defense-in-depth model was that the mobile, flexible forces of the second century that defended the perimeter with forward offensives launched from lightly defended bases were now replaced with part time peasant soldiers who played a purely static, defensive role. These former soldiers were called the “limitanei,” which represented, along with their field fortresses, the new defense of an empire denuded of a central or even regional reserve incapable of surging to meet military or diplomatic crises. Luttwak concludes, “with this, the output and input of the system are finally equated. The level of security provided becomes directly proportional to the amount of the resources expended on the army and on the frontier fortifications. The great economy of force that made the unitary empire a most efficient provider of security is lost.”
In closing, I would recommend this book only to those who have a basic familiarity with Roman history and the experience of the frontier. It is written in a style that suits the general reader, but I suspect the gravity of the argument and conclusion will be lost on those who are reading about the Empire for this first time in this volume.
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