For nearly three centuries after their first clash in 54 вс, the Parthians were the most dangerous opponents the Romans faced in the eastern part of the Empire. The Parthian military system and philosophy was radically different from the Roman and their army relied almost exclusively on cavalry. There were Parthian infantry, most of whom were said to have been archers, but they were of poor quality and receive very little mention in our sources. The strength of the Parthian army lay in its two types of cavalry, the heavily armoured cataphracts and the light horse-archers. It was the latter who most encapsulated the Parthian military philosophy. Horse-archers were unarmoured and would stage a mounted charge only as a last resort against an enemy who was already weakened. Instead, they used their powerful composite bows to shoot down their enemies and the mobility of their swift horses to avoid contact and make themselves difficult targets for return fire. Firing from a moving horse did not make for accurate shooting, but the objective was to pepper the target area with as many arrows as possible so that some were bound to find a mark. Only when the enemy had been weakened by this constant barrage would the cataphracts charge and break them. If the enemy’s strength and determination seemed undiminished then the Parthians withdrew and continued to shadow their opponents, waiting for a more favourable opportunity. The Parthians would certainly flee if the situation was unfavourable. The readiness with which the Parthians fled but then rounded on any incautious pursuers always astonished the Romans. It made it very difficult to inflict a decisive defeat on them in battle since it was so easy for the enemy horsemen to escape. In 36 вс Mark Antony’s soldiers were dismayed to discover that a Parthian rout and vigorous Roman pursuit produced only thirty dead and eighty' prisoners.
This scene from the Column shows Roman cavalrymen pursuing defeated Sarmatian cataphracts. Both horses and riders are depicted as completely covered in a mesh of metal scales, a fanciful reconstruction of a type of soldier which the sculptor had perhaps never seen. These heavy cavalry evidently impressed the Romans for Hadrian formed the first regular cataphract unit in the Roman army and others were created in later years.
The wars between Rome and Parthia tended to focus on the same few border regions, the client kingdom of Armenia and the valleys of the Euphrates and Tigris. Trajan mounted a massive effort in a final attempt to defeat the Parthians and led his troops as far as the Persian Gulf. However, rebellions began to erupt in the land to his rear and it was whilst busy suppressing these that the emperor fell ill and died.
When the Romans and Parthians first encountered each other in battle at Carrhae in 53 вс, both sides were overconfident. The Romans had grown used to brushing aside the armies of Armenia and Pontus with consummate ease. The greater part of the Roman cavalry and light infantry rashly pursued a Parthian withdrawal, became separated from the main force, were surrounded and annihilated. Throughout the rest of the day the square formed by the legions came under a heavy barrage of arrows, the Parthians regularly replenishing their quivers from a well-organized supply of ammunition carried by the camel train. Many Romans were wounded, but the army was never weakened to the point where it could be swept aside by a cataphract charge, and the situation reached something of a stalemate. However, the Roman army and its commander lost heart and decided to withdraw, abandoning its wounded. The Parthians, ideally suited to harassing a retreating foe, especially one who was mostly on foot, pursued with vigour and nearly all of the Roman army was slaughtered or forced to surrender, the legions losing their precious eagles. This complete success encouraged the Parthians to despise Roman armies, especially since the force at Carrhae represented only part of their strength and had been expected to delay and not to defeat the enemy. Their attempted invasion of Syria ended in disaster, however, when on two occasions Parthian armies dashed themselves to pieces attacking uphill against confident legionaries supported by slingers, whose missiles might give a cataphract concussion even if they did not penetrate his armour. After this both sides treated the opponent with caution and Roman armies marching against the Parthians made sure that they included a good proportion of cavalry and infantry armed with missile weapons. Even more importantly they used all elements of the army to support each other, the heavy infantry to provide solidity, the archers and slingers to keep the enemy at a distance — bowmen on foot will usually outrange horse-archers — and the cavalry to mount carefully controlled counter-attacks. The Parthians, true to their military doctrine, would refuse to join battle with such a well- prepared force, although they would attempt to lure out and isolate for destruction any small detachments whose commanders were over bold. Skilful Roman generals kept their subordinates under tightly control when campaigning against the Parthians.
This terracotta statuette shows a galloping Parthian horse-archer about to fire his re-curved composite bow. Later Arabic manuals advised that the archer should aim to loose his arrow when his horse was in mid stride. Accuracy was to he sacrificed to deluge the target with as many missiles as possible, before the archer withdrew out of range of any return fire.
The Arch of Septimius Severns commemorated his successful Parthian expedition, during which he had sacked both Ctesiphon and Seleucia. The reliefs showing scenes from the fighting are heavily eroded, but seem to have followed the style of the column of Marcus Aurelius, which sacrificed accuracy for artistic convention.
The result was a stand off. The Romans could not force the mobile Parthians into a decisive battle and the Parthians could not prevent a well-prepared and well-handled Roman army from marching through their territory. The Romans targeted Parthian cities and strongholds, besieging and storming them one by one. The Parthian capital, Ctesiphon, was sacked several times. The Parthians exploited their mobility to attack the Romans’ supply lines, or distract their attention by deep raids into Syria or the kingdoms allied to Rome. Antony’s invasion failed when his siege-train, lagging behind the main columns and protected by two legions, was captured in its entirety. In the resultant retreat he was harassed by the Parthians and suffered enormous losses, mostly from disease and shortage of provisions. A war fought under Nero went very well for the Romans, until one poorly led army suffered a reverse, was jostled into a panicked flight and surrendered, the legionaries undergoing the humiliation of being sent under the yoke. An invasion of Parthia was a massive undertaking requiring huge numbers of troops to make the advancing armies strong enough both to deter Parthian attacks and to be able to besiege and take their cities. In addition, more soldiers were needed to protect the lines of communication that supplied the advancing forces and to defend Rome’s provinces again Parthian attacks. All these troops needed to be fed and supplied, and much of the campaigning area was not productive enough to allow the troops to support themselves by foraging, an activity which anyway left small detachments isolated and vulnerable to the mobile enemy. The size of Parthia and the time-consuming task of taking strongholds one by one until the Parthian king was forced to come to terms made an invasion an undertaking of several years. Only the emperor himself could command such an enterprise, without the probability of creating a dangerous rival, and few felt inclined to spend long years on campaign in the east. Ultimately, the scale of the task and the difficulty of finding sufficient manpower prevented a Roman conquest of Parthia, and conflicts came instead to focus on domination of the kingdoms between the two empires, notably Armenia.
The Romans initiated most of the conflicts with Parthia, save in ad 155 when the Parthian king launched an unprovoked invasion of Armenia and followed on to attack Syria. The Parthians’ lack of skill in siege warfare meant that their invasions tended to consist of large-scale raids. Parthia was always very weak internally and rarely presented a real threat to the stability of the Roman east. Theoretically the Arsacid king controlled sufficient wealth from the prosperous Hellenistic cities and the profits of the major trade routes to maintain his dominance over the aristocracy. In practice the great noble families had usurped many royal prerogatives and provided the majority of troops for the royal army, supplied in contingents on a feudal basis. In many ways it was not in the interest of the monarch for the military followers of noblemen to be too effective. Surenas, the successful commander at Carrhae, was executed because the king feared him as a potential rival. Therefore the political system prevented the army from becoming too effective. The continual renewal of war with the Parthians has been interpreted as an indication that Roman imperialism had not died with the Republic, and that the dream of world conquest and the desire to emulate Alexander the Great still motivated many emperors. The underlying cause of this hostility is simpler and was due to the Roman understanding of war which we have already discussed. The Parthians had fought and humiliated the Romans and were therefore enemies. Until they ceased to be perceived in this way by being absorbed as subordinate allies or conquered as a province, then renewal of hostilities was inevitable.