The History of Rome, Book III. Theodor Mommsen
From the earliest hour of the morning the Roman light troops had been skirmishing with the light cavalry of the enemy; the latter slowly retreated, and the Romans eagerly pursued it through the deeply swollen Trebia to follow up the advantage which they had gained. Suddenly the cavalry halted; the Roman vanguard found itself face to face with the army of Hannibal drawn up for battle on a field chosen by himself; it was lost, unless the main body should cross the stream with all speed to its support. Hungry, weary, and wet, the Romans came on and hastened to form in order of battle, the cavalry, as usual, on the wings, the infantry in the centre. The light troops, who formed the vanguard on both sides, began the combat: but the Romans had already almost exhausted their missiles against the cavalry, and immediately gave way. In like manner the cavalry gave way on the wings, hard pressed by the elephants in front, and outflanked right and left by the far more numerous Carthaginian horse. But the Roman infantry proved itself worthy of its name: at the beginning of the battle it fought with very decided superiority against the infantry of the enemy, and even when the repulse of the Roman horse allowed the enemy's cavalry and light-armed troops to turn their attacks against the Roman infantry, the latter, although ceasing to advance, obstinately maintained its ground. At this stage a select Carthaginian band of 1000 infantry, and as many horsemen, under the leadership of Mago, Hannibal's youngest brother, suddenly emerged from an ambush in the rear of the Roman army, and fell upon the densely entangled masses. The wings of the army and the rear ranks of the Roman centre were broken up and scattered by this attack, while the first division, 10,000 men strong, in compact array broke through the Carthaginian line, and made a passage for itself obliquely through the midst of the enemy, inflicting great loss on the opposing infantry and more especially on the Gallic insurgents. This brave body, pursued but feebly, thus reached Placentia. The remaining mass was for the most part slaughtered by the elephants and light troops of the enemy in attempting to cross the river: only part of the cavalry and some divisions of infantry were able, by wading through the river, to gain the camp whither the Carthaginians did not follow them, and thus they too reached Placentia.39 Few battles confer more honour on the Roman soldier than this on the Trebia, and few at the same time furnish graver impeachment of the general in command; although the candid judge will not forget that a commandership in chief expiring on a definite day was an unmilitary institution, and that figs cannot be reaped from thistles. The victory came to be costly even to the victors. Although the loss in the battle fell chiefly on the Celtic insurgents, yet a multitude of the veteran soldiers of Hannibal died afterwards from diseases engendered by that raw and wet winter day, and all the elephants perished except one.
Hannibal Master of Northern Italy
The effect of this first victory of the invading army was, that the national insurrection now spread and assumed shape without hindrance throughout the Celtic territory. The remains of the Roman army of the Po threw themselves into the fortresses of Placentia and Cremona: completely cut off from home, they were obliged to procure their supplies by way of the river. The consul Tiberius Sempronius only escaped, as if by miracle, from being taken prisoner, when with a weak escort of cavalry he went to Rome on account of the elections. Hannibal, who would not hazard the health of his troops by further marches at that inclement season, bivouacked for the winter where he was; and, as a serious attempt on the larger fortresses would have led to no result, contented himself with annoying the enemy by attacks on the river port of Placentia and other minor Roman positions. He employed himself mainly in organizing the Gallic insurrection: more than 60,000 foot soldiers and 4000 horsemen from the Celts are said to have joined his army.
Military and Political Position of Hannibal
No extraordinary exertions were made in Rome for the campaign of 537. The senate thought, and not unreasonably, that, despite the lost battle, their position was by no means fraught with serious danger. Besides the coast garrisons, which were despatched to Sardinia, Sicily, and Tarentum, and the reinforcements which were sent to Spain, the two new consuls Gaius Flaminius and Gnaeus Servilius obtained only as many men as were necessary to restore the four legions to their full complement; additions were made to the strength of the cavalry alone. The consuls had to protect the northern frontier, and stationed themselves accordingly on the two highways which led from Rome to the north, the western of which at that lime terminated at Arretium, and the eastern at Ariminum; Gaius Flaminius occupied the former, Gnaeus Servilius the latter. There they ordered the troops from the fortresses on the Po to join them, probably by water, and awaited the commencement of the favourable season, when they proposed to occupy in the defensive the passes of the Apennines, and then, taking up the offensive, to descend into the valley of the Po and effect a junction somewhere near Placentia. But Hannibal by no means intended to defend the valley of the Po. He knew Rome better perhaps than the Romans knew it themselves, and was very well aware how decidedly he was the weaker and continued to be so notwithstanding the brilliant battle on the Trebia; he knew too that his ultimate object, the humiliation of Rome, was not to be wrung from the unbending Roman pride either by terror or by surprise, but could only be gained by the actual subjugation of the haughty city. It was clearly apparent that the Italian federation was in political solidity and in military resources infinitely superior to an adversary, who received only precarious and irregular support from home, and who in Italy was dependent for primary aid solely on the vacillating and capricious nation of the Celts; and that the Phoenician foot soldier was, notwithstanding all the pains taken by Hannibal, far inferior in point of tactics to the legionary, had been completely proved by the defensive movements of Scipio and the brilliant retreat of the defeated infantry on the Trebia. From this conviction flowed the two fundamental principles which determined Hannibal's whole method of operations in Italy—viz., that the war should be carried on, in somewhat adventurous fashion, with constant changes in the plan and in the theatre of operations; and that its favourable issue could only be looked for as the result of political and not of military successes—of the gradual loosening and final breaking up of the Italian federation. That mode of carrying on the war was necessary, because the single element which Hannibal had to throw into the scale against so many disadvantages—his military genius—only told with its full weight, when he constantly foiled his opponents by unexpected combinations; he was undone, if the war became stationary. That aim was the aim dictated to him by right policy, because, mighty conqueror though he was in battle, he saw very clearly that on each occasion he vanquished the generals and not the city, and that after each new battle the Romans remained just as superior to the Carthaginians as he was personally superior to the Roman commanders. That Hannibal even at the height of his fortune never deceived himself on this point, is worthier of admiration than his most admired battles.
Hannibal Crosses the Apennines
It was these motives, and not the entreaties of the Gauls that he should spare their country—which would not have influenced him—that induced Hannibal now to forsake, as it were, his newly acquired basis of operations against Italy, and to transfer the scene of war to Italy itself. Before doing so he gave orders that all the prisoners should be brought before him. He ordered the Romans to be separated and loaded with chains as slaves—the statement that Hannibal put to death all the Romans capable of bearing arms, who here and elsewhere fell into his hands, is beyond doubt at least strongly exaggerated. On the other hand, all the Italian allies were released without ransom, and charged to report at home that Hannibal waged war not against Italy, but against Rome; that he promised to every Italian community the restoration of its ancient independence and its ancient boundaries; and that the deliverer was about to follow those whom he had set free, bringing release and revenge. In fact, when the winter ended, he started from the valley of the Po to search for a route through the difficult defiles of the Apennines. Gaius Flaminius, with the Etruscan army, was still for the moment at Arezzo, intending to move from that point towards Lucca in order to protect the vale of the Arno and the passes of the Apennines, so soon as the season should allow. But Hannibal anticipated him. The passage of the Apennines was accomplished without much difficulty, at a point as far west as possible or, in other words, as distant as possible from the enemy; but the marshy low grounds between the Serchio and the Arno were so flooded by the melting of the snow and the spring rains, that the army had to march four days in water, without finding any other dry spot for resting by night than was supplied by piling the baggage or by the sumpter animals that had fallen. The troops underwent unutterable sufferings, particularly the Gallic infantry,
Polybius's account of the battle on the Trebia is quite clear. If Placentia lay on the right bank of the Trebia where it falls into the Po, and if the battle was fought on the left bank, while the Roman encampment was pitched upon the right—both of which points have been disputed, but are nevertheless indisputable—the Roman soldiers must certainly have passed the Trebia in order to gain Placentia as well as to gain the camp. But those who crossed to the camp must have made their way through the disorganized portions of their own army and through the corps of the enemy that had gone round to their rear, and must then have crossed the river almost in hand-to-hand combat with the enemy. On the other hand the passage near Placentia was accomplished after the pursuit had slackened; the corps was several miles distant from the field of battle, and had arrived within reach of a Roman fortress; it may even have been the case, although it cannot be proved, that a bridge led over the Trebia at that point, and that the -tete de pont- on the other bank was occupied by the garrison of Placentia. It is evident that the first passage was just as difficult as the second was easy, and therefore with good reason Polybius, military judge as he was, merely says of the corps of 10,000, that in close columns it cut its way to Placentia (iii. 74, 6), without mentioning the passage of the river which in this case was unattended with difficulty.
The erroneousness of the view of Livy, which transfers the Phoenician camp to the right, the Roman to the left bank of the Trebia, has lately been repeatedly pointed out. We may only further mention, that the site of Clastidium, near the modern Casteggio, has now been established by inscriptions (Orelli-Henzen, 5117).