Makers of Ancient Strategy: From the Persian Wars to the Fall of Rome (47 page)

therefore, a much greater deficiency in Luttwak’s analysis is his lack

of attention to how Rome’s frontier assets—the combination of for-

tifications and troops he so insightfully identified—were actually used

in practice in the late Roman period of the third and fourth centuries.

For right through to the end of the fourth century, Roman forces did

not merely wait for the barbarians, sitting behind belts of formidable

frontier fortification like some equally doomed precursor of the French

and the Maginot Line. Such a sequence of events did unfold along the

228 Heather

frontier on occasion, as in the case of the Saxons in 370, for instance,

but far too infrequently for it to count as the dominant strategy that

the Romans employed for maintaining frontier security. Such a strategy

would not in any case have proved very effective. To economize on

pay, equipment, and supplies, many units of the mobile armies were

kept at such a low state of readiness unless a campaign was actually

in the offing, and slow speeds of movement made for such slow re-

sponse times, that there was a substantial danger that even quite large

barbarian raiding forces would be safely back across the frontier long

before any effective counterstrike could be launched. Everything ex-

cept messages could move no faster than about 40 km per day, and to

ease the problem of supplying them, even the mobile troops were not

quartered in very dense clusters. To concentrate a decent force against

any attack and then get the troops to a point where they could actually

intervene was generally a matter of weeks rather than days, so that a

purely responsive strategy would always leave raiders with plenty of

opportunity for pillage and withdrawal.7 I suspect, in fact, that it was

precisely to buy the time he needed to mobilize sufficient troops that

the local Roman commander went through the sham of concocting his

pseudo-agreement with the Saxon raiders of 370.

When the narrative historical sources are added to the evidence of

military archaeology and known troop deployments, a very different

picture of overall Roman strategy emerges. Forts and armies were

only two elements of an approach to frontier management that relied

extremely heavily on a manipulative repertoire of diplomatic intru-

sions, backed by the periodic deployment of main force. The typical

pattern that emerges from late third- and fourth-century sources is

that whenever the political-military situation along a particular frontier

zone threatened to get out of control, a major campaign, often led

personally by a reigning emperor, would be mounted beyond the impe-

rial border. The Tetrarchic emperors of the late third and early fourth

centuries mounted a succession of such campaigns on all three main

sectors of Rome’s European frontiers: the Rhine, Middle Danube (west

of the Iron Gates), and Lower Danube (to the east). Constantine I cam-

paigned on the Rhine in the 310s, and in the Lower and Middle Danube

regions in 330s. His son Constantius II (together with his cousin and

Frontier Defense 229

caesar Julian) led armies east of the Rhine and north of the Middle

Danube in the 350s, while in the next decade Valentinian and Valens

again led substantial military forces over the frontier in both the Rhine

and Lower Danube regions.8

As recounted in the surviving narrative sources, these campaigns

tended to follow a similar script. Any overly mighty barbarian leaders

were first subdued, and then, for a period, the Roman armies set to

burning down every settlement they could find.9 But the deeper pur-

pose of this kind of military action was not destruction per se, although

the campaign certainly had a deliberately punitive purpose, as well as

being good for military morale, since it allowed the troops to pillage at

will. The effects of regular Roman pillaging of frontier areas are also

occasionally visible archaeologically.10 Nonetheless, the actual Roman

campaigning was no more than the precursor to the campaigns’ main

purpose, which was to force all the higher- and medium-level barbarian

leaders of the affected region formally to submit to imperial authority.

Once a sufficiently dominant display of aggression had been deemed

to have occurred, the emperor would typically establish his camp, and

the regional barbarian leaders would troop in one by one to make their

submissions. This process is again explicitly described on a number of

separate late Roman occasions, from the Tetrarchic emperor Maximian

in the 290s to Constantius II and Julian in the 350s and beyond.11 How

far into barbarian territory beyond the frontier these campaigns tended

to range is not clear. They could certainly last several weeks, however,

and I suspect that at least their diplomatic effects—in the form of ac-

quisition of territories belonging to the procession of submitting kings

and princes—were felt for a distance of about 100 km beyond the impe-

rial frontier.12

The emperor and his advisers then set about turning short-term

military dominance into longer-term security, as the example of Con-

stantius II’s manipulations in the Middle Danube region in the 350s

effectively illustrates. First on the agenda was a survey of current bar-

barian political confederations in the affected region. If any were too

large, posing too great a threat to frontier security, they were broken

up, with subleaders being handed back their independence from the

overly mighty king to whom they currently owed allegiance. In the

230 Heather

Middle Danube of the 350s, for instance, Constantius was clearly wor-

ried about the power of a certain Araharius, and freed some Sarmatian

vassals led by Usafer from his control. He also elevated the prince of

another group of Sarmatians, Zizais by name, to royal status and re-

newed the political independence of his following. This independence

was backed by guarantees of Roman military support and reinforced

by targeted annual diplomatic subsidies to reinforce more favored

leaders’ positions. It has sometimes been argued that these subsidies

were “tribute” and a sign of late imperial weakness. As a diplomatic

tool, however, they had been in constant use since the first and second

centuries, when Roman dominance was pretty much absolute, and in

the fourth century they were granted even to barbarian leaders who

had submitted. They should clearly be understood in modern terms,

therefore, as targeted aid, designed to shore up the power of Rome’s

chosen diplomatic partners.13

While all this diplomatic maneuvering was under way, any Roman

captives held in the region were released, and forced drafts of man-

power were taken from the submitting barbarians as recruits for the

Roman army.14 At the same time, these periodic emperor-led interven-

tions were usually undertaken in response to some reasonably sus-

tained bout of frontier trouble. Because campaigning on this scale was

expensive, it usually required a major sequence of disturbances to act

as a trigger. Even aside from the Roman troops’ pillaging, therefore, it

was entirely common for the renewed agreements to contain punitive

clauses, with those held to be the guilty parties being punished in a

variety of ways. On occasion, this could even mean a barbarian king’s

execution. In 309, for instance, Constantine I executed two kings of

the Franks in the theater at Trier.15 More usually, however, the desire

for revenge was satisfied by imposing various financial penalties, most

commonly in the form of exactions of labor and raw materials for re-

building work, along with substantial quantities of food supplies.16

From time to time, emperors might use their military superiority to

take much more drastic action. Aside from breaking up dangerous polit-

ical structures on the other side of the frontier, emperors were also con-

cerned to ensure that no frontier region became overcrowded. This was

a situation that could and did lead to the internal rivalries of different

Frontier Defense 231

barbarian leaders spil ing over onto Roman soil. One response was to

force—at sword point, if necessary—some of the empire’s immediate

neighbors to abandon their established homes and move away from the

frontier zone. In the Middle Danube of the 350s, for instance, Constan-

tius II decided that one particular Sarmatian subgroup, the Limigantes,

was to be expel ed, and was entirely happy to use force to make them

leave. Another response was to al ow particular barbarian groups to be

received onto Roman soil on strictly regulated terms. The Tetrarchs in

particular employed such control ed resettlements on al the major Eu-

ropean frontiers in the two decades after 290 AD, but this technique had

an established prehistory and continued in use subsequently.17

This is not to say that Rome’s repertoire of manipulative diplomatic

techniques was always deployed as part of an entirely coherent or ra-

tional policy for frontier defense in what might be termed a “grand

strategy,” with the emphasis firmly on “grand.” As we have seen, in-

ternal political agendas sometimes made emperors pick fights where

there was no need, so that they could show off to their taxpayers. In

reality, too, all the major cross-border campaigns of the late imperial

period tended to be responsive, coming after the breakdown of order

within a particular frontier region, rather than because political and

military intelligence indicated that order was about to break down.

When assessing the overall effectiveness of Roman frontier defense,

therefore, it is necessary to factor into the equation that substantial

economic losses to outside raiding were also part of the picture, since

it took a fair amount of raiding to trigger a response. How substantial

that raiding might have been has emerged from an exciting archaeolog-

ical find made while dredging in the Rhine near the old Roman frontier

town of Speyer. Late in the third century, some Alamannic raiders had

been trying to get their booty back home across the Rhine when their

boats were ambushed and sunk by Roman river patrol ships. This booty

consisted of an extraordinary 700 kg of goods packed into three or four

carts, the entire looted contents of probably a single Roman vil a, and

the raiders were interested in every piece of metalwork they could find.

The only items missing from the hoard were rich solid silver ware and

high-value personal jewelry. Either the lord and lady of the house got

away before the attack or else the very high-value loot was transported

232 Heather

separately. In the carts, however, was a vast mound of silverplate from

the dining room, the equipment from an entire kitchen (fifty-one caul-

drons, twenty-five bowls and basins, and twenty iron ladles), enough

agricultural implements to run a substantial farm, votive objects from

the vil a’s shrine, and thirty-nine good-quality silver coins.18 If this haul

represents the proceeds of just one localized raid, the magnitude of

the more sustained disturbances required to trigger an imperial cam-

paign should not be underestimated. Nonetheless, the overall pattern

of the evidence is unmistakable. Late Roman emperors did not leave

their troops passively behind the frontier merely waiting for trouble.

Periodically, the field armies were trundled out in force to establish an

overwhelming level of immediate military dominance, which was then

used to dictate an overall diplomatic settlement for the region that was

in line with the empire’s priorities, to maximize the cost-value ratio of

the original campaign.

In addition, a further subrepertoire of intrusive techniques was then

used to shore up each diplomatic settlement and increase its effective

life span. Targeted annual subsidies, designed to keep favored kings in

power, were common. Particularly favored groups would also receive

special trading privileges. Normally, trade was allowed only at a few

designated points in any frontier segment, but occasionally the empire

would throw in an open frontier to sweeten a deal. After his defeat in

of the Gothic Tervingi on the Lower Danube in the early 330s, for in-

stance, the emperor Constantine I opened up the entire spread of their

sector of the Lower Danube for trade. This was done by the emperor

from a position of strength, as something designed to give these Goths,

or their leaders who would benefit from the tolls, real reason to keep

the peace.19 It was also customary to take high-status hostages, usually

the sons of kings and princes, as a further prop to any peace deal. If

things went wrong, these captives could be executed, but there is only

one known fourth-century example of this. More generally, these hos-

tages were usually also young, and bringing them up around the impe-