Roman Ideology on Warfare: The Background to Recruitment II: Continued Offence

While the river frontiers - Rhine, Danube, Euphrates - became increaingly fixed against expectation, this does not mean that the Romans gave up offensive operations to hide behind their defences. Emperors were still expected to wage foreign campaigns. Caligula had every intention of conquering Britain in 39, deduced from his raising of two new legions and when Claudius finally did in 43, it was a substantial undertaking including 20,000 legionaries plus a similar number of auxiliaries. Nero was prepared to invade Parthia in order to settle the Armenian conundrum. The redistribution of the legions by the Flavians shows the extent of Rome’s continued offensive stance. Eight were stationed along the Rhine, six in the Danubian provinces and another six in the east (Keppie (1984), 194 – four were subduing Britain, two in Egypt and one each in Spain and Africa). Domitian annexed the Agri Decumates while Trajan exemplified Roman belligerence by conquering Dacia and Parthia (However, Trajan’s annexing of Armenia and large parts of Parthia revealed problems with prolonged Roman advances in the east. These peoples had long established cultural and national identities unlike any Rome had encountered in the west (Luttwak (1976), 45-46)).

The reign of Hadrian is usually seen as a milestone in Roman frontier strategy through “the establishment of a linear barrier of perimeter defence” (Ferrill (1986), 25). While it is true that barriers were erected in the Agri Decumates, the fossatum Africae and northern England, they did not form an all encompassing structure. Neither is it accurate to describe them as linear (An aerial view of Hadrian’s Wall shows how well-supported by roads, forts and villages not only to the south but also to the north it was (Collingwood Bruce (1978); Mann (1979), 180)). The idea of a more defensive Rome is further weakened by the reign of Antoninus Pius who conquered lowland Scotland, establishing his own wall between the Firths of Forth and Clyde, and enlarged the Dacian province. However, even if it was not the institution of a coherent grand strategy of wall building, something had changed on the frontiers in the century since Augustus. The Empire was more militarised than ever before with the frontiers manned directly by the legions and all client states had been annexed.

The remainder of the second century saw the Empire continue to fight offensive campaigns. Marcus Aurelius was prepared to annex Bohemia; Avidius Cassius reached Dura-Europus and crossed the Euphrates into Osrhoëne and Septimius Severus conquered Mesopotamia by advancing the eastern frontier to the line created by the Jabal Sinjār mountains, and the Khābūr and Tigris rivers. However, these advances were cases of reactive rather than pre-emptive offence (Mann (1979), 180). Marcus Aurelius campaigned into Bohemia only after expelling the Marcomanni and Quadi from Italy, while Avidius Cassius was retaliating against a Parthian invasion in 162 (Dio LXXI.2; SHA. Marcus Aurelius 8; Millar (1993), 111). Even the conquest of Mesopotamia has been suggested as a defensive measure because Syria had proven vulnerable (Luttwak (1976), 108; Salway (1981), 227-31 suggests that Severus’ British campaign was defensive in nature; on the other hand Isaac (1992), 394 notes that the annexation of Mesopotamia did not prevent the sack of Antioch by Shāpūr I in 256 and goes further to suggest that Rome’s presence across the Euphrates may have caused Sassanid aggression). However, such thinking would have required a change in the traditionally obdurate Roman mindset. It is much more likely that the dream of Alexandrian conquest was still alive in the late second century. However, reactive offence continued during the third century. From the death of Caracalla and the accession of Diocletian, all Roman campaigns in the east were in reaction to action by the Persian kings Ardashīr and Shāpūr I. Usurpations and invasions left the Empire cutting a poor figure by the late 260s with only Africa, Illyricum and Italy recognising the authority of Gallienus. This led to new military thinking and the emergence of mobile armies for a more reactive defence. The subsequent reconquests of Aurelian and Probus show the effectiveness of such strategically-placed, highly mobile forces.

Despite these trials and tribulations, the Empire maintained an offensive stance. In 230, sixteen legions were stationed along the Rhine/Danube, ten in the east, three in Britain with one each in Spain, Italy, Africa and Egypt. While the specific lay out of the legions in the early fourth century is difficult to ascertain, some continuity is detectable. From the positioning of legionary forts (Tomlin in Brewer (2000), 169; Coello (1996), 50-58; Casey (1991), 14-15), the general lay out of the army remained similar to the 230s with large concentrations on the Rhine, Danube and the east (Jones (1964), 57). However, the literary, documentary and archaeological evidence for the disposition of the army in the frontier zones can be misleading. Written sources provide only a single moment in time whereas the Roman army could constantly be on the move or changing through campaigns and detachments. Many archaeological sites are only partially excavated, so it is dangerous to draw conclusions from what is an incomplete investigation.