Into effect. As we have noted, Julius Caesar saw the empire as

providing a protection from the distant enemies that Rome feared

– particularly, the German tribes who lived east of the Rhine, and

the Parthians beyond the Tigris and Euphrates. The fears generated

by these peoples were considerable; in the late republican

period (in 54 and 36 bc) legionary standards (‘eagles’) were twice

lost to the Parthians, and it took a considerable exercise of diplomacy

on Augustus’ part to achieve their return. Thereafter, a

broad understanding existed between Rome and Parthia on the

need for agreement on the chief bone of contention between them

– who should rule in the kingdom of Armenia, which effectively

constituted the ‘buffer’ between the two powers. Nonetheless,

crises were not uncommon in the area – for example, when Trajan

(ad 98–117) instituted large-scale plans for conquest and probably

precipitated difficulties elsewhere in the empire by diverting

troops to the area. This may have lain behind the evident instability

in Britain that preceded the building of Hadrian’s Wall. There

was always the threat, therefore, that carefully contrived balances

in other areas would be disturbed by the need to respond quickly

to upsurges of difficulty in sensitive theatres: generally, for political

and economic reasons, increasing the total number of troops

under arms was not regarded as an acceptable option.

The dangers in Europe were highlighted by the loss of three

entire legions east of the Rhine in ad 9; this disaster left on the

Roman consciousness a long-standing fear of the uncontrollable

power that lay in central and eastern Europe. Although Augustus

was probably looking to establish a European frontier as far east as

the river Elbe, he settled in the end for one which separated

Romans and barbarians by means of the rivers Rhine and Danube; on his deathbed in ad 14, he is said to have issued to his successor

the warning that the empire should be held within its existing

boundaries. Thus, to the west and south of these lines provinces

(or military districts) and client kingdoms were established to

speed the process of Romanisation, whilst units of the

army (legions and auxiliaries) were put in place at intervals to

defend the frontiers from outside attack and to look inwards as

‘police forces’ and to act in the role of a ‘pioneer corps’.

The ‘weak point’ in the European frontier – the ‘gap’ between

the head-waters of the Rhine and Danube – was eventually closed

off with a complex of fortifications including roads, forts, turrets,

ditches and palisades, strongly reminiscent of those which were

being put in place between the Tyne and Solway at the turn of the

first and second centuries ad. The care that the Romans took with

this ‘European frontier’ was amply justified as the pressure built

up along it from the late first century, eventually of course becoming

unstoppable. Again, the decision to invade Britain in the first

place was, at least in part, related to the need to maintain the

territorial integrity of this ‘buffer’ of territory to the west and

south of the Rhine and the Danube.

As we have seen, it was politically dangerous and economically

unacceptable to keep an unlimited number of men under arms;

thus, cooperation with local people had to play an important role

in making the ‘buffer’ effective. It is significant that the old

republican notions of the empire being a field in which the senatorial

aristocracy could win military glory was modified in the Pax

Romana of Augustus; the ‘new view’ was aptly summarised by

Virgil in his epic poem, the Aeneid (VI. 853):

Your task, Roman, and do not forget it, will be to govern the

peoples of the world in your empire. These will be your arts –

and to impose a settled pattern upon peace, to pardon the

defeated and war down the proud.

Chauvinism had given way to something which was, outwardly at

least, more respectable: a mission to bring civilisation to the

world.

The broad concept did not change greatly until the third century;

the number of legions across the empire remained in the region of 28–30, although obviously, as Romanisation developed,

the catchment area for the recruitment of Roman citizens into the

legions broadened too. The auxiliaries, who in Augustus’ time

had been mostly local groups under their own commanders, were

more obviously integrated into the army structure. The ‘ethnic

exclusiveness’ of units was probably watered down by local

recruiting, and in time units of Britons were enrolled amongst the

auxiliaries. The command-structure, too, was tightened, with

officers of auxiliary units being drawn from Romanised personnel

of equestrian (or ‘middle-class’) status. By the early second century

ad, the auxiliary units, through Romanisation, had become