A few days for rest and refreshment of the army were imperatively needed, but only a very few could be spared. Hannibal could not hope to face his antagonists without a large increase to his army, and this increase he could only get for the moment from the Gauls, the people in whose country he was, though later on reinforcements might be expected from Carthage. The Gauls would be ready enough to join him, for they were permanently hostile to Rome; but they would have to be satisfied of his strength. A war had opportunely broken out between the Taurini (Turin) and the Insubres (Milan). Hannibal took the part of the latter, and stormed a stronghold of the Taurini. From that moment he could practically command the services of as many Gauls as he wanted. But he had now to meet the Romans for the first time in the field.
P. Cornelius Scipio, one of the Consuls of the year, had had the province of Spain allotted to him. His intention had been to dispute the passage of the Rhone, but Hannibal had moved with such rapidity that Scipio found himself anticipated. The Carthaginians were already across the river when Scipio reached its mouth, and had secured so long a start that it was useless to follow him. But the news of the Carthaginian's arrival in Italy seemed to demand instant action. He handed his army over to Cnæus, his brother and second-in-command, reserving for himself a few picked troops only, and sailed for Italy, where he took over the division under the charge of the prætor Manlius. He marched as rapidly as possible to Placentia (Piacenza), where he crossed the Po, and advanced up the left bank of the river till he reached the Ticinus (Ticino), one of its tributaries. Over this stream he threw a bridge, which he protected by building a fort. Hannibal was encamped some ten miles to the westward, at a spot called Ictumuli, and had sent out Maharbal in command of some Numidian cavalry to ravage the country; sparing, however, all the territory belonging to the Gallic tribes. Maharbal was recalled when the advance of the Romans became known, and Hannibal moved out of his camp, in personal command of his cavalry. Scipio did exactly the same. The battle that ensued was therefore wholly a battle of cavalry. This put the Romans at a great disadvantage. They were distinctly inferior in this arm, and the nature of the country, an expanse of unincumbered plain, gave the enemy every opportunity of making the best of the advantage. Scipio had put some light-armed troops in the van. They seemed to have been of the poorest quality, for they fled at the first impact of the two armies. The regular cavalry of the Romans showed to better advantage. They held their own for some time against their assailants, also a force of regular cavalry. But they were at a great disadvantage. The fugitives from the front had thrown their lines into disorder. These it was impossible to keep firm when those panic-stricken creatures were trying to find their way through them. Then there happened a great misfortune. Scipio was so seriously wounded that he had to give up the command. According to the most generally received account, he was saved from capture by the valour of his son, then a lad of eighteen. We shall hear of him again, for he became in later years the great hero of the war, Scipio Africanus the elder.
Some of the Roman cavalry made a determined stand round their wounded chief and contrived to carry him off the field. But the battle was lost. The defeat, however, was not so complete that the Roman camp was in any danger. Hannibal, who was still hampered by his scanty numbers, was content to rest on the field of battle. That night the Romans hurriedly retreated to Placentia, hoping to find their bridge unbroken. They had actually reached their destination before Hannibal became aware of their departure. He was in time enough, however, to capture some six hundred stragglers whom he found lingering on the left bank of the Po. A great raft had been constructed for the passage of the river, and they were at work in loosing it. Hannibal came upon them while they were so employed. He captured the men, but the raft, which it would have been a great advantage to secure, floated down-stream. Two days were spent in looking for a practicable ford. Before this could be found the Roman army had recovered its order and confidence. It suffered, however, a most damaging blow within the next few days. A body of Gallic auxiliaries, two thousand infantry, and two hundred cavalry, deserted to Hannibal, cutting down the sentries at the camp gate. The Carthaginian general gave them a hearty welcome, and held out to them great promises of advancement and reward. For the present he sent them to their homes. The best service, in his judgment, that they could do was to spread abroad the report of his generosity and of the Roman defeat.
Scipio now moved southward, falling back to a position near the river Trebia, a tributary of the Po, which flows into it on its right or southern bank. Here he fortified a camp, and sat down to await the arrival of Sempronius, his colleague in the Consulship, who had been recalled from his province (Sicily) to take part in the defence of Italy. He was suffering greatly from his wound, and was unequal to the active duties of command, which, however, he was unwilling to hand over to a substitute. Probably it would have been unconstitutional to do so, when the other Consul was within reach. Yet the prætor Manlius, in whose charge the army had originally been, was probably in the camp. Constitutional forms, as we shall see again and again, weakened the military energies of Rome. Nothing could be imagined more absurd than that the army should have been entrusted to generals, changed every year, and elected by popular vote. To oppose such men to the unequalled genius of Hannibal was to ensure defeat. The mere permanence of the Carthaginian command gave him an immense advantage. But we must never forget the other side of the case. Without these constitutional forms neither Rome nor Greece (about which the historian has to say much the same thing) could have been what they were. We must expect to find in a nation as in a man the defects of its great qualities.
Sempronius joined his colleague some time, it would seem, during the month of November. He was all for action. "It is intolerable," he urged, "that Italy should be invaded and Rome threatened in this fashion. And what are we waiting for? There is no third army that can join us. Our men will lose all heart if we let them sit in their camp while the enemy plunders our friends." All this is natural enough, especially when we know that the Romans had very little idea, so far, of what Hannibal really was. But Livy, doubtless, is right when he adds that Sempronius had before his eyes the approaching election of Consuls. On the 1st of January ensuing he would have to go out of office, and yield up his command. If he was to gain the distinction of a victory he must strike at once.
He was encouraged by success in an affair in which he had engaged against the more prudent counsels of his colleague. He had strongly urged the duty of defending the friendly Gauls, had overruled the opposition of Scipio, and had actually carried off the honours of victory in a considerable cavalry skirmish.
Hannibal's plan was sufficiently simple. He was well aware—for what we should now call his "intelligence department" seems to have been admirably managed—of Sempronius's eagerness for battle. In the country that lay between the two camps was a spot which seemed admirably suited for an ambush; the bed of a stream, closed in on either side by steep banks, and enclosing a considerable space of level ground, thickly covered with bush. Here he put his brother Mago with a picked force of 2,000 men, composed of equal numbers of cavalry and infantry. "You have an enemy," he said in dismissing them, "who is blind to these stratagems of war." How familiar the words have been made by recent experiences, of our own! These arrangements made, Hannibal sent his Numidian cavalry at dawn the next day with instructions to ride up to the Roman camp, to pour a shower of missiles upon the sentries, and, if possible, to provoke an engagement. Sempronius was, he knew, eager to fight. This insulting demonstration would stir the temper of the men in such a way that they would obey with enthusiasm a command to advance. The device was completely successful. Sempronius led forth his men in hot haste after the Numidians, who retreated in apparent disorder. The Romans, thus hurriedly summoned, had not had a meal; their horses had not been fed; and they suffered from cold as well as from hunger. It was a snowy day in November, and the region, the marshy, low-lying ground between the Alps and the Apennines, had an inclement climate. More than this, they had to cross the river, whose waters, swollen by the autumn rains, and now breast high, struck a piercing cold into their limbs. When they emerged on the other side of the stream they could scarcely grasp their weapons.
Hannibal's men were in very different case when they were led forth to encounter the enemy, warmed by fires in their tents, and strengthened by a leisurely meal. The order of battle was this. The slingers were in front; on either wing the cavalry and the elephants; in the centre the heavy-armed infantry. The total number is given by Polybius at about forty thousand. Half of these were infantry, Spaniards, Africans, and Gauls, these last representing the addition which Hannibal had been able to make to the army of the Alps. The cavalry numbered more than ten thousand. Here also Gauls appear as "Celtic allies." Of the slingers there were eight thousand. The Roman force was almost exactly equal, but differently made up. It had but four thousand cavalry, as against ten thousand. Of the infantry, sixteen thousand were Romans, and twenty thousand auxiliaries.
It was among the light-armed and the cavalry that the first signs of disorder and weakness could be seen. They were specially depressed by suffering and exhaustion. A light-armed soldier is nothing if he has lost his mobility, and this is exactly what had happened to the Romans. They could render little or no help to the heavy-armed, whose flanks and front were alike exposed, without any kind of covering, to hostile attack. The centre, nevertheless, offered a stout resistance to the enemy. For a time they held their ground manfully, and in one direction did more than hold it. A body of ten thousand men broke through the Carthaginian line, and steadily made their way to Placentia, where, of course, they were in safety. Of the rest of the army few survived. Their line was first broken by the unexpected charge of the ambushed force. This was actually in the rear of the Roman infantry, and the attack which they made from behind on the legions, occupied as they were with what was going on in front, was very destructive.
Many, also, were crushed by the elephants, which gave valuable help to their side, not, however, without some counterbalancing mischief. The animals, once wounded, became unmanageable, and were quite as likely to damage their friends as their foes. This was, indeed, the last as well as the first occasion on which Hannibal used them, for the cold was so severe that all but one perished. We may sum up what is recorded of the effectiveness of the elephant in ancient warfare by saying that his first appearance was terrifying, that experience greatly lessened the fear with which he was regarded, as the means of dealing with him were soon learnt, and that he was always an incalculable and unreliable force.
The season was now far advanced, considerably beyond the time when it was usual to suspend military operations for the year. Hannibal retired into winter quarters, though his cavalry never ceased to scour and ravage the country. At Rome there was much alarm, shown, however, in a resolute attempt to do all that was possible in the way of preparation for the future.