A summary of my debate post, as requested by some users. Please take note that this is a much abbreviated version and should not be in any way be regarded as the equivalent of my debate post.
My general arguments against his study were as follows:
a) Out of the twenty centuries during which a roman state existed, Luttwak only concentrated on four, thereby missing important clues which undermine his arguments like army dispositions in the fourth century
b) It is doubtful whether the romans had any notion of grand strategy at all, since they had no word for strategy at all. Words like defence-in-depth or even strategy are a modern invention.
c) Luttwak argues that the deployment of forces primarily had the focus of defending the empire. This is more than questionable. The primary motive of the Romans was not defence of the empire, but expansion.
d) It is also doubtful if Luttwak really understands the roman army. He ignores the integration aspect of the army. Auxillaries, for example, served the purpose of integrating the subjugated peoples as well as providing the empire with specialist forces or more manpower. In the east, the Roman army in Judea primarily served as a peacekeeping force, troop deployment was dictated by the necessity in face of revolts or political developments, not by an outside threat. He completely ignores the importance of the roman army with the civil administrations of provinces. The Roman army assisted with tax collection, infrastructure projects and performed administrative functions and did not only exist to defend the empire.
Luttwak said that the defence of the system was handled according to three systems:
The Julio-Claudian Model, which was in use since the ascension of Augustus to the Throne up until the time of the Flavian emperors, stationed the highly mobile legions inside the empire, acting as strike-forces if needed. Defense was first and foremost left to an outer ring of client states, who absorbed the impact of the enemy assault. Since security needs can be fulfilled by the clients, this results in enormous disposable surplus strength of the empire, which paves the way for future expansion.
His first system rests on the assumption that clients were profitable and that indirect rule (clients) was favored to direct rule (provincialization) in the period from Augustus-Nero. Against this I argued that:
- There was no single trend towards direct or indirect rule. Both Augustus and Tiberius alternated between the two forms according to the situation at hand.
- There is no direct evidence to assume that the client states were profitable. In fact, when cappadocia was provincialised, the Romans expected a huge raise in revenue, something that had not been available as a client. The final argument against the efficiency of the client system is the fact that the Romans provincialised almost every client kingdom.
- it is more than questionable if the Romans ever pursued a client policy in Germany as they did in the east. The practice of resettling allied or subjugated tribes (Ubians, Treveri) or placing legions directly in their territory is anathema to Luttwak's theory. Clients on the northern frontier caused the loss of seven legions and had to be kept in check by substantial expenses.
The second stage, ranging from the time of Vespasian until the end of the Severan Dynasty, heralds the end of the client system, which are almost all absorbed by the empire. Legions are now stationed near the firmly drawn frontiers, whereas only weak clients remain. Strong clients are no longer tolerated due to their threat to the empire itself. Defense is forward in nature and aims to deal with enemies before they reach the frontiers of the empire. This system, according to Luttwak, results in no disposable surplus strength – strength has to be taken by drawing away forces from other frontiers in order to secure future expansion.
Against this I argued:
- the notion that this system had no disposable surplus strength has to be dismissed. In fact, during the time period, 11 legions were formed. It is also questionable if the Roman empire only had a brief “surge capacity”, as Luttwak asserts. This is easily countered by the fact that the new legions were permanent formations.
- forward defence is nothing new to teh empire, having been practiced since the time of the republic. In fact, the orginal meaning of limes is "fortified road into enemy territory".
- Unlike Luttwak suggests, the roman army of this period is at least as flexible as the Augustean army, as evidenced by the war of 161. Luttwak makes the mistake to assume that just because legions did not change their base frequently, they must have been static in nature. In fact, Roman legions had become even more flexible in unit organization. The widespread use of the formation known as the vexillatio now permitted individual detachments from one legion to become attached to other legions, even permanently if necessary.
- There is no evidence that any frontier was overstressed, as Luttwak claims
- Following the empire's success in dealing with the deadliest enemies of the period, it might be argued that in this timeframe, Rome was even stronger than under the Julio-Claudians. For example, the parthian capital was sacked thrice in this timeframe and romans even had diplomatic contact with China, having led armies way into media themselves.
- The roman empire expanded into the north and even more so in the east, thereby disproving the concept of static frontiers
The third system arises out of the turmoil of the third century and is finalized under Diocletian. Abandoning the notion of forward defence, invaders now have to be stopped by a complex system of defense in depth. This system is necessarily inferior to the second system, since it neither provides for a surge capacity nor for any disposable military surplus strength to be used against appearing threats. The failure of this system marks the end of the Western Roman empire.
- the posture of the empire was not primarily defensive in nature and there is no evidence that the ideology of the empire has changed in that regard.
- It is quite unlikely that the Romans had the geographical skills necessary to formulate a defense-in-depth. Roman maps are not made according to topographic reasons, but according to travel distances between cities and population centers.
- There is no archeological evidence to support a change from forward defense to defense-in-depth - in fact, archeological evidence rather supports the offensive nature of troop deployments and fortifications
- Roman forts were still positioned in enemy territory, in non-roman territory
- The only armies that could have stopped invading barbarians quickly enough when applying Luttwak's model were the regional field armies, most of which were not formed until well after Luttwak's period of choice ends (the field army of Illyrium, for example, might have been formed as late as 409 AD). Stilicho's practice of creating small reserve armies is also way too late for Luttwak to notice it.
- At least the elite parts of the Roman field armies had the primary purpose of defeating usurpers, not defending the empire against the barbarians
- in the third century, marauding bandits could mostly only be stopped after they tried to cross the border back into their lands, another argument against the existence of a defence-in-depth
- roman forces usually penetrated several hundred miles deep into german territory, once more highlighting the offensive nature of the roman army
- literary sources describe campaigns as offensive in nature and do not mention a system of defence-in-depth.