In the second century ad the army contained between 170,000 and 180,000 legionary troops and perhaps 220,000 auxiliaries.9 But there were no more than three legions in any one province, and Britain had one of the largest provincial armies with a combined strength of about 50,000 legionaries and auxiUa. The legions operated essentially as heavy infantry. The auxilia provided cavalry, various specialist missile-throwers, and also infantry, though sometimes equipped in a distinctive way. In the army of the Republic, cavalry had often been a weak point; for example, Roman defeats at the hands of Hannibal owed something to the Carthaginians’ significant superiority in this arm. Part of the problem was the expense and difficulty of maintaining large numbers of horses in Italy. In the early Republic the constitution provided for only 1800 cavalry at public expense. Rome therefore recruited cavalry from her Italian allies, but experience taught enterprising Roman commanders to look for more efficient cavalry forces elsewhere. Numidians were popular, and Julius Caesar made particular use of units of Gallic and German cavalry, often under the command of native princes. In the imperial period, these troops were gradually incorporated into the formal structure of the army in alae, equipped with spear, sword and shield.10 Occasionally special cavalry was still employed; for example, the famous Moorish cavalry under the command of Lusius Quietus, who served Trajan and rose to become consul and governor of Judaea.11 The total number of cavalry in the Roman army is difficult to recover since it is impossible to trace all the auxilia units in service at any one time. However, there were cavalry alae stationed in all provinces with legionary troops, and in Mauretania Caesariensis, which had no legionary troops, there were substantial cavalry forces of around
4000 men. The army had perhaps up to 50,000 cavalry serving in the second century ad.12 The praetorians, the emperor’s personal bodyguard, were 10,000 strong, grouped in cohorts, and a detachment usually accompanied the emperor on campaign. However, although they were equipped as elite heavy infantry, there is little sign that they made any specific tactical impact on the battlefield. Each legion had a number of siege engines,13 and more siege equipment could be built on campaign. The structure of the army permitted it to achieve typical Roman war objectives, namely to bring major enemy forces to a set battle, defeat them, and make further resistance impossible by investing and capturing their strongholds or cities.
In general the Romans did not use diplomacy to recruit military allies for their wars. They did not regard other peoples to be of sufficient standing and military capability. However, the Romans did sometimes require foreign peoples by the terms of a peace settlement to supply troops. When Marcus Aurelius negotiated terms with the Iazyges they were obliged to supply 8000 cavalry, some of whom were immediately sent to Britain.14 In the later empire, however, it became increasingly common for the Romans to employ barbarians, even former enemies, to fight for them. These people, who presumably used their own fighting methods, were then settled in the empire.15
In all periods emperors expected friendly kings theoretically independent but within the orbit of Roman influence to supply troops on demand for campaigns.16 The most striking example in the early empire was the creation by Augustus c. 25 bc of the legion XXII Deiotariana from the army of King Deiotarus of Galatia, which he had equipped and trained on the Roman model.17 On a more limited level, when, in 25 bc, Augustus ordered the invasion of Arabia under the prefect of Egypt, Aelius Gallus, the force consisted of legionaries, auxilia, 500 men from King Herod and 1000 from Obodas, king of the Nabataeans.18 Similarly, c. ad 135 when Arrian the governor of Cappadocia organized resistance to the invasion of the Alani, his force as well as regular Roman troops comprised allied forces from Lesser Armenia and Trapezus, and spearmen from Colchis and Rhizion.19 Because of the scarcity of our evidence it is possible that the Romans had this kind of support on many more occasions than we know about. Nevertheless, it seems unlikely that such support was ever decisive in achieving the Roman army’s objectives. The Romans in the main relied on their own military resources.
Augustus finally won control of the Roman world in 31 bc at the naval battle of Actium, and he went on to establish Rome’s first permanent navy, which was based eventually at Misenum and Ravenna, guarding the western and eastern coastlines of Italy. Subsequently, more squadrons were based on rivers and coasts where the Romans were militarily active, principally in Germany, Britain, on the Danube and on the Pontic sea. The total force rose to about 30,000, recruited from non-citizens in the provinces. The fleet conveyed officials and dignitaries, and also supplies for the army. It assisted in the suppression of piracy and could also act as troop transports.20 For example, in ad 66, Cestius Gallus sent a detachment of his troops by ship to take by surprise the coastal city of Joppa.21 Occasionally the fleet acted as an integral part of combined operations, as when Germanicus launched a campaign against the German tribes beyond the Rhine, and sailed part of his force through the North Sea and then up the river Ems. But this was not a complete success because of poor weather and storms.22 Campaigns against Parthia, which usually involved an attack on the capital Ctesiphon, were sometimes assisted by naval operations on the Euphrates or Tigris, with the ships serving presumably as troop transports and carriers of supplies.23 Normally the Roman navy did not spearhead military operations, was not an integral part of military strategy, and did not contribute to decisive victories. In the first three centuries ad there is no record of any significant naval battle, or any account of what life was like at sea in a warship. The Romans’ control of the Mediterranean area depended on the power of their army and their domination of the territory around its shores.
A soldier’s experience in battle depends on the nature of warfare. Roman troops would normally be engaged in external campaigns, that is, traditional warfare against militarily inferior peoples outside the empire or on its periphery, with the object of punishing or conquering them. Here the Romans often faced tribesmen who relied on a single headlong assault, or in the east highly skilled Parthian cavalry and archers. The Roman army could normally be expected to win these battles, though sometimes such encounters might create new tactical problems. Civil war by contrast set skilled Roman armies against each other armed with the same kinds of weapon and using the same tactics and stratagems. There might be higher casualties and destruction and devastation within the empire itself. Wars fought among fellow-soldiers also brought a questionable moral dimension, and perhaps also problems of motivation. Tacitus illustrates this with an anecdote from the civil wars in Italy in ad 68 to 69. A son unwittingly fatally wounded his own father, and they recognized each other as the son was searching his semi-conscious victim. When other soldiers noticed what had happened, ‘throughout the battle lines ran a current of amazement and complaint, and men cursed this most cruel of all wars. However, this did not stop them from killing and robbing relatives, kinsmen and brothers.’24 The Roman army also fought internal wars as a virtual army of occupation, in which it put down bandits and local rebellions, conducted police operations, and in some cases consolidated recently conquered areas. In certain parts of the Roman world it might indeed be difficult to distinguish between a state of war and peace. For example, in Judaea there was endemic violence and ideological resistance to Roman rule, and the Jewish rebellions in 66 to 70, 115 to 117 and 132 to 135 amounted to full-scale war.25
World History
