Cannae

by Adrian Goldsworthy

  We do not know precisely how deep the Roman centre was at Cannae, and various suggestions have been made, usually ranging from about fifty to seventy ranks. In some cases the lower figure has been based upon the assumption that the triarii were left in the main camp. Polybius’ statement that the maniples were ‘many times’ deeper than wide is fairly vague, but it is difficult to see it being applied to a formation much wider than five or six files across and less deep than twenty-nine or twenty-four ranks. If we assume that each maniple had a frontage of five men and a depth of twenty-nine then it would have occupied an area of 5m by 58m. The gaps between maniples in the same line were normally equivalent to the frontage of a single maniple, but at Cannae this was significantly reduced. Assuming an interval equal to half the width of a maniple, then the ten maniples of hastati in one legion at Cannae would have occupied about 75m by 58m, and the entire first line of the army about 1,050m by 58m. To cover the same frontage the principes would have been in an identical formation, but the less numerous triarii formed around ten to twelve deep, giving a total depth to the Roman centre of perhaps seventy-four ranks. If those scholars who suggest a somewhat shallower formation of around fifty ranks are closer to the mark, then the frontage of the infantry centre would have to be expanded to around 1.5km.

  The Roman centre at Cannae concentrated an exceptionally large number of men on a very narrow frontage and it is important to understand why such an unorthodox deployment was adopted. In any formation only the legionaries in the front rank could effectively employ their weapons. Soldiers armed with long spears might be able to reach the enemy from the second rank, but only the triarii at Cannae were equipped in this way. Men in the ranks behind the first could throw missiles over the men in front, although restricted visibility must have made it difficult to aim and it was a question of hoping to hit somewhere in the enemy mass. The pilum, the heavy throwing spear carried by legionaries and perhaps some allied soldiers, had a maximum range of just under 30m and was most effective at about half that distance. Therefore any soldiers in the ranks behind the eighth in a Roman maniple would have had difficulty in throwing their pila without running the risk of hitting their own front ranks. A deep formation did not offer the most effective use of a unit’s weaponry which could best be served by a much shallower formation of perhaps two or three ranks, with the front rank to do the actual fighting and the others to replace casualties. Yet such shallow formations were exceedingly rare and most military theorists felt four ranks to be the minimum and recommended six or eight. Shallow formations tended inevitably to be wide, and the wider a unit’s frontage, the harder it was to move across the battlefield at any speed and remain in formation. A broader formation encountered more obstacles, since no battlefield was ever perfectly flat, and required a good standard of drill and the close supervision of its officers to prevent a unit from falling into disorder. As a result, over any distance, a narrower, deeper column would move more quickly whilst retaining its order than a wider, shallow line.

  There were other reasons why troops tended to fight in deeper formations, which went beyond the purely practical. A column many ranks deep was an intimidating sight as it approached the enemy, even if many of the men within it would not actually be able to fight. As importantly, the close proximity of their comrades all around them encouraged the men forming the column. There appears to be a strong herd instinct within human beings, so that even today there is a marked tendency for men under fire to bunch together for mutual comfort, despite the fact that this tends to make them more of a target. Only rigorous training has proved able to control this instinctive reaction. The physical presence of their comrades encouraged men, but also made it difficult for them to flee. The front rank could not run until all the other ranks behind them had given way. The men in the centre and rear of the formation were removed from actual physical danger in direct relation to the depth of the formation. Deeper formations did not fight any better than shallow formations, but they did possess longer endurance in combat, simply because it was that much more difficult for the actual fighting men in front to escape. Greek military theorists recommended placing the best and bravest soldiers in the front and rear ranks, the former to do the actual fighting and the latter to prevent the rest of the unit from escaping. We cannot be sure whether or not they had this function in the third century BC, but in the latter Roman army the centurions’ second in command, the optiones, were stationed at the rear of a century to prevent the men from running away, if necessary physically forcing them back into place with their symbol of office, the hastile staff. An especially deep formation was one way of keeping questionable troops in the battle for a longer period, increasing the chance that the enemy’s morale would crack first. Throughout the ancient world, and indeed for much later military history when troops continued to fight in close formation, there was a direct link between the quality of troops and the depth of their formation. Highly trained and well motivated soldiers were able to fight in much shallower formations than was ever possible for less experienced and poorly drilled units.14

  The inexperience and lack of training of much of the Roman army at Cannae in part explains the decision to form them in such depth. It would have been exceptionally difficult to keep together a more conventional and shallower triplex acies formation, with each of the three lines stretching for several kilometres. The reduction in the frontage of each maniple and even more importantly of the intervals between them removed much of the manipular formation’s flexibility, but it did make it possible to move so many men in a more coordinated manner. The great depth also gave the Roman infantry phenomenal staying power, making it extremely difficult, if not impossible, for an enemy to defeat them in a straightforward frontal attack. Finally we must remember that the Romans’ formation may have been limited by the ground chosen for the battle. According to the above calculations, the entire Roman army occupied a frontage of about 2km or 2,100 yards (360m for the Roman cavalry, 1,050m for the infantry centre, and 540m for the allied cavalry = 1,950m). Precision cannot be claimed for a figure based upon so many conjectures and assumptions, but even if this is something of an underestimate it would still suggest that the Roman army was more than capable of being fitted into the area between Cannae and the presumed more northern course of the Aufidius. Delbrück and Lehmann, the chief advocates of a battlefield on the left bank, similarly calculated the frontage of the Roman army as under 2km in which case it could have fitted into a plain between two physical obstacles which protected its flanks.15

  The Roman plan for the battle was simple and unsubtle, but not unreasonable or by any means inevitably doomed to failure. At Trebia a large section of the Roman legions had cut their way straight through the Punic centre, defeating not just Gallic warriors, but also the Africans, Hannibal’s best infantry. At Trasimene, in spite of the massively unfavourable position and lack of organization, the Roman heavy infantry had held off the enemy attacks for hours and inflicted significant losses upon them. Throughout the same period, the Roman and allied cavalry had performed consistently badly, winning only a few minor engagements. In this battle the Romans were once again outnumbered in cavalry but had a massive advantage in infantry. It was therefore logical to rely most upon their foot in the coming battle. The problem they faced was how to bring the weight of their infantry to bear without exposing its flanks to Hannibal’s superior and mobile cavalry which had so easily swept around the Roman flanks at Trebia and robbed them of any real advantage gained by breaking the enemy centre. The answer, and it seems the reason why Varro chose to fight on the opposite bank of the River Aufidius to where Hannibal had offered battle, was to deploy not in a wide open plain, but in a narrower, more confined space. In this way the left wing was protected by the hills around Cannae and the right by the river. Although heavily outnumbered, the Roman and allied horse could not be outflanked and the enemy cavalry would be forced to attack and defeat them in a frontal charge. The Roman wings were not required to beat the e
nemy, but simply to stay in position for as long as possible. They were there to give sufficient time for the massed infantry in the centre to deliver an overwhelming hammer blow against Hannibal’s foot. If the Punic centre could be overwhelmed, then it would matter little if the Roman wings at last gave way, for on their own the Carthaginian cavalry would not be able to do much more than harass the legions. The selection of the ground at Cannae was intended to allow the heavy infantry to smash their Punic counterparts. We do not know whether Varro alone or perhaps with the assistance of Paullus, Geminus or some of the other experienced men with the army conceived this plan. It was not complicated or especially imaginative, and in fact the very close formation of the Roman foot sacrificed the usual tactical flexibility of the legions. Elsewhere Polybius commented that the Romans as a race tended to rely instinctively on ‘brute force’ (bia) when making war and that sometimes this had led to terrible disasters. Their plan at Cannae would seem to be a prime example of this trait.16

  The cavalry wings were the vulnerable spots, for they needed to remain in place long enough for the infantry to win. This was always going to be difficult, for infantry combats seem usually to have lasted for hours, whereas cavalry encounters were faster and more fluid. It was no coincidence that the two consuls took direct command of the wings, Varro leading the allies on the left and Paullus the Romans on the right. That Paullus was stationed with the citizen cavalry rather than the allies has been one of the chief arguments put forward for claiming that it was he who held overall command on 2 August, since it is assumed that this was a more prestigious post than controlling the non-citizen allies. This is in fact extremely tenuous, for there does not appear to have been any set place from which a Roman consul was supposed to lead the army. Most certainly there was no convention for where each consul should be when both were present with the army, for this was such a rare event. Roman generals tended to station themselves wherever they felt that they could do most to influence the battle and thus usually where they anticipated its crisis to occur, hence the consuls’ presence with the cavalry at Cannae. The centre was placed under the command of Servilius Geminus. There were also many tribunes and prefects, so that the Roman and allied foot were led by a very large number of senior officers concentrated along a small frontage. We do not know how the legions and alae were arranged. Livy says that the Roman legions were on the right and the allied foot on the left, but it is hard to know what to make of this. Conventionally the legions held the centre and the alae were split on either side, but there was no precedent for an eight legion army to know whether this would be followed in these circumstances. One possibility is that the different armies formed up side by side, so that the legions and alae used to working with each other remained together. One attractive idea is that the centre of the line was formed by the proconsuls’ forces, so that the best and most experienced troops formed the heart of the Roman attack, but once again this is purely conjectural. Whatever the precise details, the unprecedentedly large Roman host can only have presented an intimidating sight to the watching Carthaginians.17

  The Romans could not be sure that Hannibal would accept their offer of battle in this confined position, hence the strong force left outside the larger camp. It is even possible that Varro did not expect the Carthaginian to fight and saw this largely as a morale-boosting operation for his own soldiers, rebuilding their confidence after the humiliation of the day before. This is certainly possible for such gestures were common before the battles of this period, but it is far more probable that the Romans did want to fight the battle on this ground of their own choosing. Whatever their intentions, the sources imply that Hannibal ordered his army to move out almost as soon as he saw Varro’s columns leaving the main camp. The Carthaginian sent out his light troops to form a protective screen for the main body. This was standard practice for most armies and it is more than probable that the complicated process of forming up the Roman army was carried out behind a line of velites and perhaps some of the cavalry. Polybius noted that Hannibal’s army crossed the Aufidius at two points, which makes it very likely that it was divided into two columns for deployment. The Carthaginians then formed into battle order, probably within a kilometre of the Roman line.18

  Hannibal is said to have had 10,000 cavalry and 40,000 infantry at Cannae, but we have no precise figures for the various contingents making up this total. The cavalry were a mixture of Spanish and Gallic horse, both of whom fought in close order, and the Numidian light cavalry. The Gauls had all been recruited from the Cisalpine tribes after Hannibal arrived in Italy, and he is said to have had 6,000 Spanish and Numidian horse after crossing the Alps. At most the Numidians may have accounted for two-thirds of this total, but they must have suffered some casualties in the 218 and 217 campaigns and their strength was probably somewhere between 3,000 and 4,000. At Cannae the Numidians were placed on the Punic right flank opposite Varro and the Allied cavalry, and it seems probable that they roughly equalled these in numbers. All of the Gallic and Spanish cavalry, some 6,000–7,000 men, were massed on the left flank, giving them a numerical superiority of two or three to one over their Roman counterparts. Probably the Punic horse occupied roughly the same frontage as the Roman and allied cavalry, but it is unlikely that they were quite so densely packed. The Numidians normally fought in small, widely spread bodies which advanced and retreated in each other’s support, always avoiding close contact but harassing the enemy with missiles. The Gauls and Spaniards were almost certainly divided into several lines of squadrons, for if cavalry became too crowded then they tended to merge into one mass which was difficult for its leaders to control and inclined to panic and stampede. The behaviour of these horsemen during the battle makes it clear that they were kept closely in hand by their officers.

  Hannibal’s infantry were formed with the African foot on the flanks and the Gauls and Spanish in the centre. It is difficult to know how many men should be deducted from the total of 40,000 to account for the infantry skirmishers. He had had 8,000 of these men at Trebia and although his army had been significantly augmented by Gallic tribesmen since then it is questionable how many skirmishers these provided. The warrior culture of the Gallic tribes placed most emphasis on close fighting, and light infantry seem to have played little part in intertribal warfare. If there were still only 8,000 light troops at Cannae, then the close order foot mustered something like 32,000 men, once again divided into Gauls, Africans and Spanish. Hannibal had 20,000 foot when he arrived in Italy, consisting of the Libyans, Spanish and light infantry, and none of these contingents had as yet received any reinforcements. Perhaps there were around 6,000 light infantry, some of them Spanish, 4,000 Spanish close order troops and 10,000 Libyans. All of these had suffered some casualties by August 216. If there were 8,000–9,000 Libyans and around 3,000–4,000 Spanish at Cannae, then that would suggest something like 19,000–21,000 Gallic warriors in the main line.

  The Carthaginian centre consisted of the Gallic and Spanish foot, perhaps 24,000 men in all. These were intermingled, companies or units of each being deployed alternately. Polybius uses the Greek word speirai (spe… rai) for these units, a term which he also sometimes employs for the Roman maniple and which would later become the term used for the 480-man cohort adopted by the professional Roman army. It is doubtful that these bands were of uniform size, and anyway either there must have been more Gallic than Spanish units or each unit was significantly larger, but it is most likely that this refers to a group of a few hundred men and probably less than a thousand. The African foot were divided into two roughly equal bodies and stationed on the flanks near the cavalry. They were formed either in one deep column or in several lines one behind the other. Although this is not explicitly stated by any of our sources, it is highly probable that the Libyans were in fact behind the main line of Gauls and Spanish and concealed from the Romans’ view. The likelihood is that they formed one of the two columns used by the Punic army in its deployment. The Africans, issued by Hannib
al with captured Roman equipment, were approximately equivalent in size to two legions, one behind each of the Carthaginian army’s flanks.19

  Once all the units of the army were in place, Hannibal made one major alteration to its formation, advancing the units in the centre of the main line so that this bulged towards the enemy. The most probable interpretation of the descriptions in our sources is that the companies in the very centre of the line advanced to form a line further forward and that the companies on either side were echeloned back. It must have been obvious that the Romans were relying on the densely packed mass of infantry in their centre to win the battle. Hannibal’s foot were greatly outnumbered and in the past had had difficulty standing up to the legions even on equal terms. At Trebia Hannibal’s foot had formed a single line so that there were no reserves to plug the gap when the Romans broke through his centre. At Cannae he could have chosen to make his centre as strong as possible by concentrating all the foot into one line. Yet he could not rival the depth and therefore the endurance of the Roman infantry and in the end such a line was likely to give way. Another option would have been to copy Roman practice and divide the foot into two or more lines stationed one behind the other, so that as the troops in the fighting line became weary they could be reinforced by fresh reserves, something Hannibal would choose to do at Zama in 202 BC. However, once again, this could at best delay the inevitable Roman breakthrough. Instead of delaying the clash with this overwhelming force, Hannibal kept his centre relatively shallow and then moved it forward so that the Roman charge would reach it more quickly. His objective was to concentrate the Roman effort at the very centre of his line, knowing that it must inevitably break and that the Romans would pour through the gap they had created. Then, it was hoped, they might make themselves vulnerable to flank attacks from the Libyan foot, his best, most disciplined men. Whilst this was going on the Numidians on the left were supposed to keep the Latin cavalry busy, and at the same time the concentrated force of the Gallic and Spanish horse mounted a huge, direct attack at the Roman right. These were to smash the Roman cavalry and then, remaining in good order, threaten the rear of the Roman army.20