Ancient History & Civilisation

'Caesar... gave the signal as soon as the enemy volleys became weak and poorly-aimed, and suddenly he let loose his Cohorts and turmae. In an instant the enemy was driven back from the disputed plain...'

The African War 17-18

The Roman army, just like any other fighting force, existed to wage war. During the Principate, most soldiers spent the vast majority of their military service engaged in the peacetime routines of barracks life described in the previous chapter. Participation in active campaigning was an occasional interruption of normality, especially for troops stationed in the more settled provinces. On average the garrison of Egypt was only involved in a major campaign about once every 25 years, although many of the frontier areas experienced outbreaks of warfare far more often than this. Even when a unit did take part in operations against an enemy, most campaigns consisted of considerably more marching and labouring than actual combat. Sieges might last for months on end, but battles were rare and, with very few exceptions, decided within a single day. Most Roman soldiers probably spent only a tiny fraction of their military service on active service or actual fighting.

The Roman army’s wars were fought for a range of different reasons and on very different scales. Almost always the Romans attacked, or, if the enemy had initiated the campaign, launched a counter-offensive as soon as possible. Some wars were won when the opposing field army was brought to battle and defeated, others when the enemy capital was taken by storm or siege, and still others by repeated ravaging of crops, herds and villages. The operations of the Roman army were characterized most by its flexibility, willingness to adapt, and the determination with which it persisted in any struggle. In battle the army’s superior command structure, discipline, training and equipment gave it significant advantages over any contemporary opponent, and often allowed it to win decisive victories in the face of great numerical odds. The technical skill of the professional army also made it especially effective in siege warfare. Yet, if required, the legionaries and auxiliaries were equally adept at smaller-scale warfare, and were able to defeat enemies who traditionally fought by raid and ambush. At its best, the army of the Principate was the most sophisticated and effective fighting force until the modern era.

A battle scene from Trajan's Column showing a range of auxiliary and allied troops lighting against Dacian warriors At the bottom left is an unarmoured stinger, beside - him a bare-chested irregular, and in the top left corner a group of eastern archers

The Army at War

On Campaign

(Above) A monument, moved and restored at the end of the 1st century At) some 200 years after it was erected, commemorating the defeat of the Cimbri and Teutones by Marius in 101 BC This conflict was to prove the last time for many centuries that Rome appeared to be fighting for her very existence against a foreign enemy.

(Opposite) In this sculpture from Rome defeated barbarians beg for mercy from the Emperor Marcus Aurelius The proper end to any Roman war came when the enemy admitted defeat and surrendered, accepting whatever terms Rome chose to impose on them.

In the 3rd and 2nd centuries BC the Romans faced several opponents with regular armies which were better trained and disciplined, and sometimes better led, than the legions. Pyrrhus, the famous Greek commander hired by Tarentum to fight against Rome, defeated two Roman armies before finally succumbing in a third, hard-fought battle, whilst Hannibal’s string of successes rested as much on the high quality of his army as his tactical genius. Fortunately for the Romans, their main clashes with Macedonia and the Seleucid Empire came at a time when the legions were of exceptionally high quality, a high proportion of both officers and men being veterans of the Second Punic War. The legions produced by this generation were as confident and experienced as any professional soldiers, many having spent much of their adult life in the army, and this allowed them to exploit the greater tactical flexibility of the manipular system in comparison to the rigid Hellenistic pike-phalanx. In this period, and throughout the remainder of Rome’s history, her armies also faced many opponents from the tribal peoples. Such armies were sometimes large, but, whilst the individual fighting skills of their warriors were often high, lacked discipline and tended to be clumsy in their movements. Against such armies the Mid Republican legions usually enjoyed a slight, though by no means decisive, advantage.

By the time that the Romans had converted their citizen militia into a professional army, most of the states with regular armies had already been defeated. From the 1st century BC onwards, most Roman wars were waged against tribes or kingdoms with unsophisticated military systems. Such forces often had only rudimentary supply systems, seriously limiting the time which they could spend in the field before having to disperse. Most lacked a clear command structure, and were capable of undertaking only the simplest strategy and tactics. This meant that the professional Roman army was almost always markedly superior to its opponents. The Roman way of fighting had always tended to be very aggressive. In this period it became even more so, for Roman commanders could be fairly confident of victory even when heavily outnumbered or fighting in unfavourable circumstances. When boldness and confidence became rashness this could lead to disaster, but in most cases it produced spectacular success.

Types of war

Whenever the Romans fought a war, they fought to win, pursuing total victory with a ruthlessness and relentlessness that was unparalleled. However, the context of the campaign did much to determine the army’s behaviour. For convenience we may divide Roman campaigns against foreign opponents into four basic types:

1. Wars of conquest. This was an attack upon a socio-political group such as a tribe, kingdom, city or league of cities, or state. Victory came when the Romans had reduced this entity, turning it into a directly ruled province or subordinate client state. How this victory was achieved varied from people to people. If the invaded state possessed a capital town/city with strong political or religious significance then its capture might well prompt a surrender. Similarly the defeat in open battle or battles of the enemy field army might trigger such a collapse. However, many tribal peoples lacked such an important centre and might not be able or willing to fight a massed battle. In this case the Romans had to adapt to fighting a lower level of campaign. Attacks could be made on individual settlements, however small, and less numerous local enemy forces brought to battle. In this case the enemy would be conquered after many much smaller reverses, rather than a single great defeat in battle or siege.

Warfare in the ancient world could often prove profitable. In addition to plunder taken from the enemy, captives could be sold into slavery. Julius Caesar is credited with lowing enslaved over a million people during his Gallic campaigns, at the end of which he was one of the richest men in the world. This relief from the principia at Maim shows barbarian captives chained by the hands and necks.

The conquest of the Belgic tribes in 57 вс is an example of one such war. Prompted by an attack on a Roman ally, Julius Caesar led his legions against the army of the Belgic tribes of northeastern Gaul. The two sides confronted each other across a narrow valley for some days, but neither proved willing to abandon their own strong position and attack the enemy at a disadvantage. The stalemate was broken when the Belgians’ food supply ran out, and their army dispersed, harried by Roman pursuit. Caesar advanced and ravaged the territory of each tribe in turn. It took some time before the Belgians once again mustered their main army, which promptly attacked the Romans as they were building a camp near the River Sambre. Despite initial surprise the Romans won a decisive victory, and all the tribes present at the battle swiftly capitulated. Contingents from some tribes had not joined the army in time and these peoples were defeated separately, Caesar besieging their main towns in turn.

2. The suppression of rebellion: This represented a war to suppress a people already within the Empire. Victory came when the rebels had been placed once again under Rome’s dominion. At the beginning of a rebellion, the military initiative inevitably lay with the rebels. In its early stages a rising would be weak, for in general much of the population would not join until some initial successes suggested that the rebels had a reasonable chance of victory. At this stage, even Roman inaction allowed the rebels’ confidence to grow, for this suggested weakness. Therefore the Roman response to rebellion was always to mount a display of force as soon as possible. Whatever troops were quickly available were mustered and sent immediately to attack the centre of the rebellion. Such forces were often numerically weak, under-trained and without proper logistic support. If they met strong opposition then this could frequently result in disaster. The Romans gambled that the rapid appearance of an army which appeared overwhelmingly confident of its success would overawe the rebels and stop the insurrection from gaining momentum. Where such initial responses failed, it was usually a case of waiting to muster a proper army and sending it to fight what was effectively a war of conquest.

The rebellion of Boudicca in AD 60 was suppressed by the Romans. Enraged by the mistreatment of their Queen and her daughters, the Iceni tribe (who occupied an area roughly equivalent to modern Norfolk) rebelled against Rome and, joined by other tribes, sacked in succession the colony of Camulodunum (Colchester), and the towns of Verulamium (St. Albans) and Londinium (London). The first Roman reaction was to despatch 200 ill-armed soldiers composed of men seconded from their unit to perform administrative and escort duties for imperial administrators. These were annihilated at Camulodunum. The second response was from a vexillation of Legio IX Hispana under the command of Petilius Cerialis, which boldly attacked the heartland of the rebellion, but this force was also defeated and, with the exception of the legate and some cavalry, massacred. Finally, the provincial legate, Suetonius Paulinus, returned from campaigning in north Wales and brought Boudicca's host to battle. The Britons were defeated and, throughout the autumn and winter, the Roman armed launched a series of brutal punitive actions against the rebellious tribes.

3. Punitive expeditions: This was an attack on a political group which was not intended to incorporate them into the Empire in any way. Instead the object was to instil a fear of Rome’s military might in the enemy. In some cases such expeditions were justified as revenge for attacks on the Empire. (In the earlier Republic the acquisition of plunder could be a primary aim, but this was very rare for most of the period.) Punitive columns moved rapidly, causing as much devastation to settlements and property as they could. In essence they were intended to show a people that they were vulnerable to appalling attack whenever the Romans chose to launch one. Sometimes such campaigns culminated in a pitched battle, often fought when the tribes attempted to block the Romans’ path when the latter began to withdraw. Defeating an enemy army in this way could greatly add to Roman prestige. However, on other occasions the Roman force deliberately moved so quickly to avoid any confrontation. Punitive expeditions might inspire fear, but they were only ever a temporary solution and needed to be repeated fairly often. The memory of massacred people, burned villages and stolen herds was as likely to sow the seeds of future hatred of, and conflict with, Rome.

An example of punitive action occurred at Mount Amanus on the border between Cilicia and Syria in 51 вс. The proconsul of Cilicia, Marcus Tullius Cicero - more famous as an orator and author than a soldier - decided to punish the bandit tribes of the Amanus area and put together a force of two understrength legions and some local allies. Dividing them into three columns, they suddenly attacked the tribes, capturing several of their villages. The Romans then spent 57 days besieging the tiny stronghold of Pindenissus, whose eventual surrender prompted the capitulation of another nearby fortified village. The operation was intended to show the tribes that the Romans were both capable of and willing to strike at their strongest places. However, when soon afterwards the Syrian governor launched a similar expedition in this region and suffered a defeat in a skirmish this impression of Roman might was greatly weakened.

4. In response to raiding/invasion: These were campaigns fought to intercept and defeat hostile forces which had broken into the Empire. As already mentioned, the Romans needed to stop or avenge each incursion into the provinces if it was not to encourage more attacks. The reaction was in many ways similar to that inspired by internal rebellion. The locally available Roman troops moved rapidly to engage the raiders as soon as they were reported. In most cases they were unable to prevent the bands from plundering, but the raiders’ very success often made them vulnerable. Slowed down by booty, they were frequently caught as they retreated by swift- moving Roman columns and wiped out.

In ad 50 there was a raid by the Chatti on upper Germany. Several groups of Chattan warriors crossed into the Roman province and began to plunder the countryside. The provincial legate Publius Pomponius Secundus sent a small force of auxiliary infantry and cavalry ahead to cut off the raiders and to keep in contact with them while he mustered his main army. He divided this into two columns, one of which swiftly came across a band of tribesmen, most of whom were drunk, and killed or captured them. The other Roman force encountered a more organized raiding party and defeated them in a pitched battle. Secundus then led his army on an invasion of the Chatti’s own lands. The Germans declined his offers of battle and capitulated.

The early 1st-century AD Arch of Orange, southern France, commemorated a victory won over Gallic tribes. This relief from the Arch shows legionaries and auxiliary cavalrymen fighting Gallic warriors Roman convention meant that only enemy dead were shown in such battle scenes

By their very nature wars of conquest and punitive expeditions were offensive operations. However, a striking feature of the Roman response to rebellion or raiding was the desire to seize the initiative and adopt the offensive as soon as possible. Roman strategy was always bold. This did not necessarily mean seeking a massed battle. At times, Roman commanders were not confident that they could win such an engagement. Instead they chose to harass the enemy with small-scale raids or to besiege his strongholds. As significant was the flexibility of the Roman system. The army had many advantages in siege warfare and large-scale battles. Even in Late Antiquity, the Roman army won the vast majority of the battles in which it engaged. However, when required, it could wage war at a lower level, the main army dividing into a number of columns. Such small forces could move quickly and fight by raid, surprise attack and ambush. It is certainly a mistake to claim that the professional Roman army was unsuited to fighting enemies who waged guerrilla warfare and avoided open battle. In time, the Romans were always able to adapt to the local situation. The sophisticated command structure, training and well-organized supply system gave them advantages in all levels of warfare.

Field forces and army size

The Mid Republican army had functioned best at the level of the two-legion consular force which, with alae and local auxiliaries, numbered some 20,000-30,000 men. This probably remained the optimum army size for the professional army, and very few field forces numbered more than 40,000. Significantly larger Roman armies had rather a poor record, and it is probable that these were difficult for a commander to control.

The composition of a force varied from period to period and region to region. Small forces, especially those engaged in local punitive expeditions or chasing barbarian raiders, might consist entirely of auxilia, and indeed a cohors equitata was in essence a miniature army with a balance of horse and foot. Usually, however, there was a legionary component, and these units, with their higher levels of command structure, grouped as they were in building blocks of c. 5,000, provided the heart of most armies. Under the Principate, three or four legions, perhaps augmented by vexillations from others, were the largest forces likely to take the field together in anything other than a major war led by an emperor in person. There does not appear to have been any fixed complement of auxiliaries to support a legion. Tacitus mentions eight cohorts of Batavians, some apparently cohortes equitatae, which had been attached to Legio XIV Gemina during the Boudiccan Revolt and other campaigns in Britain. By contrast. Varus had only three alae and six cohorts with his three legions when these were destroyed in ad 9. The garrisons of the eastern provinces appear to have contained more units of foot and mounted archers, and large numbers of such missile-armed troops were essential for facing the almost exclusively cavalry armies of the Parthi- ans as well as nomadic tribes like the Alans. Also particularly common in the east, especially in the 1st century AD, were allied troops from the client kingdoms of the area.

A scene from Trajan's Column showing troops loading supplies onto a river barge. In keeping with the old adage that an army marches on its stomach, the Roman army derived great advantage over almost all its opponents from its highly organized system of supply This allowed properly prepared Roman legions to operate under adverse conditions and surprise opponents.

Logistics in the field

Ensuring that his army was adequately supplied was a prime concern for any Roman commander. Under the Republic a system evolved for shipping large quantities of food and material from distant provinces to supply the troops in a war zone. Apart from the details of how this was administered, much the same thing continued to occur under the Principate.

A campaigning army normally included a good deal of wheeled transport. On the bottom right of this scene from Trajan’s Column we see ox-carts carrying provisions in barrels Over to the left is a light ballista or scorpion mounted on a mute-drawn cart.

In the field, army commanders could carry necessary supplies with them, maintain supply lines to depots established in the rear, or attempt to forage for provisions from the land around. These methods were not mutually exclusive and Roman armies frequently employed a combination of them. Except in the worst desert conditions, at least some provisions could be foraged. Water was usually available, as was the firewood required to cook the army rations which were issued unprepared. Depending on the season, varying amounts of fodder for animals, and at harvest time considerable quantities of grain for human and animal consumption were available, whilst herds could be confiscated for meat. In winter there was little to be had, unless the storerooms of the native population could be found and seized. Foraging also had the disadvantage that it took time, and could lay the foragers open to ambush, but appears to have been practised on occasion throughout the period.

Small amounts of food could be carried in the soldiers’ packs, but the bulk required transport by pack animals or in carts. The army placed great reliance on mules, but also employed other pack animals, whilst draught oxen were frequently employed to pull wagons. In peacetime only a small proportion of the animals needed to mobilize the army were kept, and the remainder were bought or requisitioned when needed, so that the choice of animal may have depended on what was available locally. All types of animal obviously needed to be fed, further adding to the army’s total requirements. A basic equation determined how far any animal could travel before it would have consumed a weight of food equivalent to the amount it could carry. Mules were perhaps the most flexible, could move as fast as a marching infantryman and go virtually anywhere that he could go. Draught oxen had considerable pulling power and could usually be fed by grazing, but were very slow, and ideally needed roads or tracks of a reasonable standard. A large army, even one gathering some of its requirements through foraging, inevitably had a huge baggage train if it did not wish to be tied to supply lines and so carried the bulk of its supplies with it. Equally inevitably, such a large number of animals made its column exceptional big and so slowed the rate of march. Maintaining a clear supply line back to dumps of material still involved convoys of pack or draught animals going back and forth between this and the main army. These were vulnerable to attack, especially if the enemy was as mobile as some of Rome’s opponents, most notably the Parthians and Persians. Therefore the need to provide guards for the supply line took manpower away from the main force.

Caesar’s campaigns in Gaul provide by far the most detailed account of the supply system of a campaigning army. During these years the Romans used various combinations of the three basic supply methoda Large supply dumps were established, often with the aid of allied communities. The army also carried a good deal of material, including not just food and equipment, but records and numbers of hostages, in its main baggage train. In the campaigning area, it was not uncommon for Caesar to establish the train under guard and then lead the remaining legions out for short expeditions. During this time they moved quickly, carrying the barest minimum of supplies, a state known to the Romans as expedita. For one or two weeks an expedita column was free to manoeuvre at some speed and through difficult terrain, providing that it returned to the main baggage train at the end of this time.

Operating in winter was difficult for any army, and virtually impossible for many of Rome’s opponents. Given time to prepare, the Romans were able to operate for a limited period in spite of the season, granting them a massive advantage.

Marching camps

At the end of each day’s march a Roman force spent probably two to three hours constructing a formally laid out camp protected by a rampart and ditch. This was a routine procedure which differed only in its details from that followed by the army from at least the 3rd century вс Some modern commentators have seen this as an indication that the Roman army was a slow-moving, inflexible force, capable of waging only a form of trench warfare. This is undoubtedly a mistake, for this was really little more than the equivalent of ‘digging-in’ for a modern infantryman. The time and effort required to build a marching camp did not significantly slow the rate of march of a Roman column, which was determined to a far greater extent by the speed and endurance of its pack train. The camp offered security from surprise attacks - there is no record of one having been successfully stormed unless the Roman army had already been defeated in the open field.

The only detailed description of the layout of a temporary camp in this period is provided by the probably 2nd-century ad work normally attributed to Hyginus. This describes the area allocated to each type of unit in a highly varied field army, consisting of praetorian guard and guard cavalry, whole legions as well as vexillations, auxiliary units, detachments from the fleet and various allies. Only limited space is set aside for the baggage train, and this may be the reason why Hyginus’ camp seems comparatively small for the number of troops, especially when compared to the size of surviving marching camps. Marching camps are rarely excavated in an extensive way, since if the army only stopped there for a night or two, it is unlikely that they would have left much trace. The siege camps at Masada and elsewhere give more of an idea of the actual layout of short-term camps. These were occupied for several months, so that the soldiers built themselves low-walled huts, using the tent as a roof. Traces of these remain, and suggest that, as with more permanent bases, the layout of temporary camps varied slightly, whilst being to a recognizable pattern.

(Above) During the siege of Masada the soldiers had the time to build low stone huts using their tents as roofs. Traces of these temporary structures are visible today and can be seen in this view of Camp F. Part of this camp was employed by a smaller number of troops after the fall of the fortress and their smaller camp is in the top left comer. The huts built by these troops appear even to have had a storage room for equipment similar to the pairs of rooms occupied in a permanent barrack block.

(Above) Each contubernium of eight soldiers lived in a leather tent like this reconstructed example. The mule which carried the tent was tethered to the ground behind it.

Camps of various periods were frequently built on virtually the same site. Sometimes this may simply have been because the factors which originally made the location a good choice for a temporary camp were still obvious in later campaigns. However, it also emphasizes the Roman tendency to think in terms of routes to a place.

'A desolation called peace': winning and losing

Most wars in this period (and indeed throughout history) ended when one of the opposing sides lost the will to fight on and conceded defeat. Rarely was it possible for a side to destroy the opposition’s ability to fight on. Roman strategy was devoted to putting sufficient pressure upon their opponents to trigger this collapse of will. This might involve Roman forces targeting the enemy’s field army, its major city or cities, or attacking its villages, burning crops and seizing farm animals. When fighting against an enemy led by a charismatic leader, the Romans’ main objective became to kill or capture that individual, for without his presence resistance usually collapsed.

Devastation (vastatio) was a frequent object of punitive expeditions. The area affected was usually comparatively small, including the area covered by the column’s march and some relatively short distance either side. The experience was undoubtedly appalling for the communities within this zone, but others even a comparatively short distance away suffered no direct harm. In spite of this, the ability of the Romans to strike suddenly, wherever they chose, and with dreadful force, instilled a sense of their own vulnerability on the inhabitants of a much broader region. The Roman army’s methods were often brutal. Apart from the devastation of property and agriculture, enemy peoples faced massacre, massed crucifixion and enslavement. After the surrender of the Gallic town of Uxellodunum in 51 nc, Julius Caesar gave orders for the defenders’ hands to be cut off as a warning to others, and during the siege of Jerusalem in ad 70, the legionaries crucified prisoners within sight of the walls. Atrocities were considered acceptable by the Romans as long as they achieved some practical end and were not done simply for the sake of cruelty.


(Above) A scene from Trajan’s Column showing Roman auxiliaries setting fire to a Dacian town, abandoned by its defenders who retreat while looking back to see the destruction. Behind them is a line of Dacian fortifications, the parapets decorated with a row of severed heads mounted on poles. Over on the right a column of legionaries marches through difficult terrain. One man is shown fording a river, holding above his head his helmet, armour and equipment in his shield.

The Roman method of waging war was highly aggressive. The initiative was seized as soon as possible and maintained, continued pressure being put upon the enemy until his will to continue collapsed. Even when faced with serious reverses in the field and an apparently hopeless military position, the Romans were unwilling to admit the possibility that they might lose. Roman commanders who presided over defeats sometimes faced criticism, but the worst thing that any leader could do was not to lose, but to admit that he and Rome had lost. Any negotiations or treaties ending a war had to make clear Rome’s outright victory. The utter refusal to concede defeat - a Roman characteristic which persisted until well into Late Antiquity - made it very difficult for Rome to lose a war. In the end, persistence and continued aggression almost always brought Rome victory. Sometimes that victory reduced a people to the position of subject allies or saw their incorporation into the Empire. Less often it saw the enemy’s destruction as a political entity. At other times Rome’s victory was more a question of retrieving honour and pride lost in earlier defeats.

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