For this mixed formation to succeed, Hannibal had to understand how each contingent worked in order to make the best use of them. He also commanded the respect of the various leaders, who trusted his orders. It was a highly complex arrangement requiring intelligence, planning, and foresight. Luckily for the Carthaginian army, Hannibal possessed these qualities in abundance. He knew how to get the most from each group. He also had a handful of trusted generals. These were his brothers Hasdrubal and Mago, Hasdrubal Gisco, Maharbal, and Masinissa.
Hannibal’s army was experienced and confident; the army’s recent victories had boosted its morale considerably. The army functioned well, with the senior leaders controlling the disparate sub-units under Hannibal’s overall control. Hannibal also knew once battle was joined his influence over events was limited, so he engaged in extensive planning beforehand so his men knew exactly what to do.
While Paullus’s and Varro’s armies prepared to march, Hannibal’s army left its winter quarters at Geronium and moved toward Cannae in June 216. This was a deliberate move as the ruined fortress at Cannae was a grain and food storage site serving the entire region. Occupying the area threatened food production for the whole area, something the Romans could not ignore without appearing helpless in front of their local allies. If the Romans did respond, Hannibal would get the battle he wanted. Regardless of whether the Romans appeared or not, the Carthaginians gained. In the interim, they could nourish themselves on Roman food.
The Roman armies of Atilius and Servilius shadowed Hannibal. Word soon reached Rome that he was at Cannae. Paullus and Varro hurriedly finished their preparations and marched out in late June. The entire Roman force rendezvoused about two day’s march from Cannae, only about four months after Paullus’s and Varro’s election as consuls. It was a noteworthy accomplishment considering that Rome had never before fielded such a large army.
The Romans advanced toward Cannae and made camp five miles away, within sight of their opponents. Paullus and Varro succumbed to arguing. Paullus worried that the broad, flat plain was perfect for the cavalry actions at which the Carthaginians excelled. But Varro vehemently disagreed. As the two were alternating command each day, Varro soon had the chance to dispatch a reconnaissance in force to better ascertain Hannibal’s position. The Carthaginians responded with cavalry and light infantry and a sharp skirmish ensued. The Romans suffered initial reverses but quickly recovered, reforming their lines. They drove the Carthaginian troops steadily back until nightfall put an end to the fighting.
This was a good initial success for the Romans, but the advantage was squandered the next day when Paullus took command. He refused to launch a followup foray; instead, he split the Roman army and set up a new camp on the other side of the Aufidius River. By doing so, Paullus hoped to better protect the Roman foraging parties while menacing the Carthaginian foragers.
Sensing the approaching battle, Hannibal gathered his troops and gave a speech. He told them he had no need to ask for their bravery because they had shown it three times already in previous battles since arriving in Italy. Hannibal further reminded them of all they had achieved since then. “He who will strike a blow at the enemy—hear me!” said Hannibal. “He will be a Carthaginian, whatever his name will be, whatever his country.” The speech worked, encouraging the entire army about the battle to come.
The next day Hannibal likewise established a second camp on the other side of the river. Paullus was in command and made no response, keeping his army in its own camp. He believed he could wait out Hannibal, not wanting to fight in that location. Soon enough, Hannibal’s supplies would grow low and he would have to march. Some Romans did come out to collect water, and Hannibal dispatched a group of Numidians to harass them. This angered Varro and many in the Roman camp. The situation was bound to change the next day, though, when command of the army switched.
Varro took charge the following morning. He assembled the entire army at dawn on the south side of the river. The Romans drew up into their battle formation facing south toward the Carthaginians. Hannibal had purposely placed his troops generally facing north so that the libeccio blew dust into the Romans’ eyes. The combined legions possessed 40,000 Roman infantry, 40,000 allied infantry, and 6,400 cavalry. Varro detached 10,000 infantry from the main force to remain at the camp, leaving 76,400 to engage the Carthaginians.
The Roman line was organized with each of the four consular armies in line next to each other. The infantry closed up so that they presented a narrower front with more depth to their ranks. This may have been due to the inexperienced men in the two newest armies, who lacked the training and experience to maneuver well in the standard formation. This was not necessarily a bad arrangement, but with the armies of Paullus and Varro on the outside edges of the line, it meant the least experienced troops manned the flanks.
The Roman cavalry took position on the right end of the line, anchored on the river. The allied horsemen deployed on the left end of the line. The light infantry screened the front of the line. Paullus went with the Roman cavalry on the right while Varro was with the Allied cavalry on the left. The two previous consuls stood in the center with their respective armies.
The 50,000-strong Carthaginian army was composed of 50,000 infantry and 10,000 cavalry. Hannibal deployed his light infantry, both slingers and spearmen, to screen his army as it crossed the river. Once across the river, Hannibal anchored his left wing on the river, placing 6,000 Iberian and Gallic cavalry on the extreme left flank under the command of Hasdrubal. On the extreme right flank were 4,000 Numidian cavalry led by Maharbal. The Gallic-Iberian heavy infantry stood in the center, with Libyo-Phoenician heavy infantry on each side. The Roman army had the greater number of men, but Hannibal’s army was more experienced and had an impressive number of victories to its credit.
The Carthaginian line advanced at Hannibal’s command, with the center slightly forward so the entire line was shaped like a crescent with the depth of the line thinning out near the edges. Hannibal’s line looked mismatched as it marched forward, the Iberians in their linen tunics interspersed with the Gauls, many of whom went into battle shirtless. All of them used large oval shields as protection. It was a polyglot force but it moved well in unison.
The opposing light infantry started the battle. The Balearians used their slings, covered by the spearmen. The Roman velites and their allies fought back and the fighting broke down into a number of small, inconclusive skirmishes all along the space between the two armies, not unusual in ancient combat. Being lightly armed and armored, the light troops in the screens could not last long even against each other and soon they fell back.
Hasdrubal’s Iberian and Gaulish cavalry charged in what Roman historian Polybius deemed “true barbaric fashion,” advancing along the bank of the river toward the Roman horsemen. It was a narrow front, with the river on one side and the infantry on the other, allowing neither force any room to maneuver. Normally, cavalry in ancient times would attempt to outflank by riding around the other force or by making feints. But the constricted space precluded those kinds of maneuvers.
The two groups rode straight into each other. The opposing horsemen were tightly packed. The horses often could not move and many simply stood still next to each other while their riders hacked and slashed at nearby enemies. Some fought so closely they grappled each other off their mounts and had to continue fighting on the ground. At first the Romans managed to put up a spirited resistance, but the violence of the Carthaginian charge took its toll in Roman casualties. Soon the Romans broke and retreated back along the river bank, the only way they could go in the close quarters. Hasdrubal ordered his horsemen to give chase and they pursued, sparing no one. Paullus managed to escape with a small contingent of bodyguards and rode to the center of the Roman line.
As the Roman right-wing cavalry fled in disorder, the infantry made contact. The legions in the Roman center crashed into the Carthaginian center, which was slightly ahead of the rest of their line. Paullus realized the battle was up to the infantry and took position where he thought he could do the most good. He shouted words of encouragement to his men, urging them forward. Each side sought to gain an advantage with its weapons. Men screamed and died, their flesh torn and yielding despite the armor they wore.
At first the Carthaginian soldiers held, fighting well despite their national and tribal differences. The Iberian and Gaulish ranks were too few, leaving their line thin and without the depth needed to maintain their defense. The legions packed their line more densely and now that depth told, forcing the Carthaginians back. Soon their bulging convex line turned into a concave one just as the Roman line now became a wedge. As that wedge grew deeper the Romans on the ends of the line started to draw in toward the center and pushed even harder toward the apparent weak spot in Hannibal’s line. These were the novice troops of Paullus’s and Varro’s armies.