As the spring advanced the great magazines which Hannibal had brought with him became nearly exhausted, and no provisions could be obtained from the surrounding country, which had been completely ruined by the long presence of the two armies. It became, therefore, necessary to move from the position which he had occupied during the winter. The Romans possessed the great advantage over him of having magazines in their rear constantly replenished by their allies, and move where they might, they were sure of obtaining subsistence without difficulty. Thus, upon the march, they were unembarrassed by the necessity of taking a great baggage train with them, and, when halted, their general could keep his army together in readiness to strike a blow whenever an opportunity offered; while Hannibal, on the other hand, was forced to scatter a considerable portion of the army in search of provisions.
The annual elections at Rome had just taken place, and Terentius Varro and Emilius Paulus had been chosen consuls. Emilius belonged to the aristocratic party, and had given proof of military ability three years before when he had commanded as consul in the Illyrian war. Varro belonged to the popular party, and is described by the historians of the period as a coarse and brutal demagogue, the son of a butcher, and having himself been a butcher. But he was unquestionably an able man, and possessed some great qualities. The praetor Marcellus, who had slain a Gaulish king with his own hand in the last Gaulish war, was at Ostia with a legion. He was destined to command the fleet and to guard the southern coasts of Italy, while another praetor, Lucius Postumius, with one legion, was in Cisalpine Gaul keeping down the tribes friendly to Carthage.
But before the new consuls arrived to take the command of the army Hannibal had moved from Geronium.
The great Roman magazine of Apulia was at Cannae, a town near the river Aulidus. This important place was but fifty miles by the shortest route across the plain from Geronium; but the Romans were unable to follow directly across the plain, for at this time the Carthaginians greatly outnumbered them in cavalry, and they would, therefore, have to take the road round the foot of the mountains, which was nearly seventy miles long; and yet, by some unaccountable blunder, they neglected to place a sufficient guard over their great magazines at Cannae to defend them for even a few days against a sudden attack.
Hannibal saw the opportunity, and when spring was passing into summer broke up his camp and marched straight to Cannae, where the vast magazines of the Romans at once fell into his hands. He thus not only obtained possession of his enemy's supplies, but interposed between the Romans and the low lying district of Southern Apulia, where alone, at, this early season of the year, the corn was fully ripe.
The Romans had now no choice but to advance and fight a battle for the recovery of their magazines, for, had they retired, the Apulians, who had already suffered terribly from the war, would, in sheer despair, have been forced to declare for Carthage, while it would have been extremely difficult to continue any longer the waiting tactics of Fabius, as they would now have been obliged to draw their provisions from a distance, while Hannibal could victual his army from the country behind him. The senate therefore, having largely reinforced the army, ordered the consuls to advance and give battle.
They had under them eight full legions, or eighty thousand infantry and seven thousand two hundred cavalry. To oppose these Hannibal had forty thousand infantry and ten thousand excellent cavalry, of whom two thousand were Numidians. On the second day after leaving the neighbourhood of Geronium the Romans encamped at a distance of six miles from the Carthaginians. Here the usual difference of opinion at once arose between the Roman consuls, who commanded the army on alternate days. Varro wished to march against the enemy without delay, while Emilius was adverse to risking an engagement in a country which, being level and open, was favourable to the action of Hannibal's superior cavalry.
On the following day Varro, whose turn it was to command, marched towards the hostile camp. Hannibal attacked the Roman advanced guard with his cavalry and light infantry, but Varro had supported his cavalry not only by his light troops, but by a strong body of his heavy armed infantry, and after an engagement, which lasted for several hours, he repulsed the Carthaginians with considerable loss.
That evening the Roman army encamped about three miles from Cannae, on the right bank of the Aufidus. The next morning Emilius, who was in command, detached a third of his force across the river, and encamped them there for the purpose of supporting the Roman foraging parties on that side and of interrupting those of the Carthaginians.
The next day passed quietly, but on the following morning Hannibal quitted his camp and formed his army in order of battle to tempt the Romans to attack; but Emilius, sensible that the ground was against him, would not move, but contented himself with further strengthening his camps. Hannibal, seeing that the Romans would not fight, detached his Numidian cavalry across the river to cut off the Roman foraging parties and to surround and harass their smaller camp on that side of the river. On the following morning Hannibal, knowing that Varro would be in command, and feeling sure that, with his impetuous disposition, the consul would be burning to avenge the insult offered by the surrounding of his camp by the Numidians, moved his army across the river, and formed it in order of battle, leaving eight thousand of his men to guard his camp.
By thus doing he obtained a position which he could the better hold with his inferior forces, while the Romans, deeming that he intended to attack their camp on that side of the river, would be likely to move their whole army across and to give battle. This in fact Varro proceeded to do. Leaving ten thousand men in his own camp with orders to march out and attack that of Hannibal during the engagement, he led the rest of his troops over the river, and having united his force with that in the camp on the right bank, marched down the river until he faced the position which Hannibal had taken up.
This had been skillfully chosen. The river, whose general course was east and west, made a loop, and across this Hannibal had drawn up his army with both wings resting upon the river. Thus the Romans could not outflank him, and the effect of their vastly superior numbers in infantry would to some extent be neutralized. The following was the disposition of his troops.
The Spaniards and Gauls occupied the centre of the line of infantry. The Africans formed the two wings. On his left flank between the Africans and the river he placed his heavy African and Gaulish horse, eight thousand strong, while the two thousand Numidians were posted between the infantry and the river on the right flank. Hannibal commanded the centre of the army in person, Hanno the right wing, Hasdrubal the left wing; Maharbal commanded the cavalry.
Varro placed his infantry in close and heavy order, so as to reduce their front to that of the Carthaginians. The Roman cavalry, numbering two thousand four hundred men, was on his right wing, and was thus opposed to Hannibal's heavy cavalry, eight thousand strong. The cavalry of the Italian allies, four thousand eight hundred strong, was on the left wing facing the Numidians.
Emilius commanded the Roman right, Varro the left. The Carthaginians faced north, so that the wind, which was blowing strongly from the south, swept clouds of dust over their heads full into the faces of the enemy. The battle was commenced by the light troops on both sides, who fought for some time obstinately and courageously, but without any advantage to either. While this contest was going on, Hannibal advanced his centre so as to form a salient angle projecting in front of his line. The whole of the Gauls and Spaniards took part in this movement, while the Africans remained stationary; at the same time he launched his heavy cavalry against the Roman horse.