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"Battle of the Trebia", in Wikipedia.

The Battle of the Trebia (or Trebbia) was the first major battle of the Second Punic War, fought between the Carthaginian forces of Hannibal and the Roman Republic in December of 218 BC, on or around the winter solstice. It was a resounding Roman defeat with heavy losses, and yet some 10,000 and more Romans, over 2.5 legions, survived on the field and retreated in order to Placentia (Piacenza). In this battle, Hannibal got the better of the Romans by exercising the careful and innovative planning for which he was famous. The impetuous and short-sighted opposing general, the consul Tiberius Sempronius Longus, allowed himself to be provoked into a frontal assault under physically difficult circumstances and failed to see that he was being led into a trap.

The battle took place in the flat country of the Province of Piacenza on the left bank of the Trebbia River, a shallow, braided stream, not far south from its confluence (from the south) with the Po river. The battle is named for the river. Although the precise location is not known for certain, it is generally accepted as being visible from the Via Emilia, now paralleled by highway A21/E70 and a railroad trunk line, all of which come from Piacenza, a contemporaneously placed Roman colony (though perhaps on an existing settlement), and cross the river north of where the Romans did in the battle. The area is possibly in the comune of Rottofreno at its main settlement, San Nicolò a Trebbia.

The two main sources on the battle are the History of Rome by Livy (Book XXI) and Histories of Polybius (Book III:69-74). The two vary considerably in some of the geographical details and are ambiguous about some key points, especially whether the Romans were camped on the left bank or the right bank of the Trebbia and in which direction they crossed the river. Reconstruction of the disposition is the major scholarly concern regarding the battle. The sources all agree on the outcome.

Contending views stem from the confusion of real and hypothetical events, beginning with the supposed “union” of the two consular armies, which Sempronius had been ordered to effect. He was advancing “with all speed to join Publius”. From the evidence, the supposed union amounted only to Sempronius having “many close conferences with Scipio, ascertaining the truth about what had occurred, and discussing the present situation with him”.

Whether the union went any further is questionable. The two consuls maintained widely separated camps. Polybius assumes a union of troops would have been effected and Sempronius would be commanding four legions (he uses conditional language and not declarative statements). He explains how after the defeat, Sempronius’ army fell back on Placentia but neglects totally to say what happened to the wounded Scipio and how he got to Placentia. Livy, on the other hand, although repeating Polybius’ numbers, states that, after the battle, Scipio quietly marched his army into Placentia and went on to Cremona so that there would not be two armies wintering in Placentia.

If Scipio’s army were intact and quietly marched into Placentia, it is unlikely that either consul commanded any of the troops of the other nor did they assist one another in any way; in fact, there is no evidence that Sempronius informed Scipio that he was going to attack. He is reported to have asked Scipio his advice on whether to attack and was strongly advised against it. There is no account at all of Scipio handing over any troops. If, as many authors suppose, Hannibal was trying to prevent a union, he seems singularly unaware of it. He made no move to stop Sempronius coming up from the east. The consuls themselves, however, each jealously guarded his own authority.

Starting with Polybius, some military writers throughout the centuries have assumed that because union was intended it was effected: this assumption leads to the problem known as “the Roman Camp”. In fact there was not one camp, but two — Scipio’s camp in the hills on the left bank and Sempronius’ camp in the plains on the right bank. Neglect of this duality leaves the writers free to select either (or neither) as “the Roman Camp”; consequently, it appears now on the left bank, now on the right; now in the hills and now on the plain. […]

After the light-armed infantry (velites) retreated through the Roman line, the Roman infantry (Hastati, Principes, Triarii) closed with the Carthaginian infantry. Concurrently the Carthaginian cavalry and elephants attacked the Roman and Italian cavalry, sweeping them from the field, and leaving the infantry, whom they intended to protect, exposed. Samuels suggests that in describing the Roman cavalry as being a withdrawal he is being tactful and a rout better describes what happened. Seeing that the Roman rear had passed their position, Mago’s hidden force emerged from the ambush and fell on the rear of the hard-pressed Roman infantry. With their morale already sapped by cold, hunger and fatigue, the Romans on the sides and in the rear broke formation under this fresh onslaught and ran for the river.

As the disorganized men were milling about the river, Hannibal used the opportunity to effect a massacre. The great majority of the casualties fell here or drowned in the river. The Roman cavalry escaped on horseback. As the Roman soldiers remained with Sempronius in the center and majority of the force were the 20,000 Italics, the men who died were probably not the core of the army but were on the whole the Italic allies, who were as yet untrained and untested in battle.

It is clear from the odds and from subsequent events that Tiberius intended a main attack on the center of the Carthaginian line. As he was not killed on the flanks or in the rear, he must have been commanding the center in person. It would have included his most experienced and effective infantry. In fact, they behaved as professional soldiers,[24] some of them quickly wheeling to fill in the sides and rear, forming a hollow square. In this standard Roman infantry formation, all sides faced outward leaving the center necessarily hollow, where the command post was and where the wounded were placed. This square soon deflected all Carthaginian attacks against it. The Carthaginians concentrated on the men by the river instead.

A light-infantry detachment was sent out to stop the elephants. These they dealt with by volleying darts and jabbing under the tail. The elephants became wild, attacking both sides, until Hannibal ordered them driven off to the left to attack the Gauls fighting for Rome. These must have been the Cenomani tribesmen, the only Gauls in that category. What Livy means by “the left” is not clear, but they cannot have been in the square and most perished.

Although he had made some unfortunate strategic decisions, Tiberius proved himself a better battlefield general, ordering his men forward against the Carthaginian center. The enemy there took great losses, although the authors do not say what they were. Of the two ethnic groups, Africans and Celts, the latter are said to have lost the most men. The square soon found itself at the Carthaginian rear and looking back could see the Carthaginian army effecting a slaughter of allied troops. Tiberius did not return to their assistance – the sources offer his excuses of the river and the heavy rain – but marched his men into Piacenza, probably over a bridge that must have stood where the highway and railroad bridges now stand.

If the Roman camp was on the left bank, then the early sequence is all wrong and one must presume even more information was omitted from the story.

The next night, according to Livy, “the camp garrison and the other survivors, mainly wounded men, crossed the Trebia on rafts.” Scipio was in command. He “marched his army in perfect quiet to Placentia, whence he crossed the Po to Cremona, that a single colony might be spared the burden of two armies in winter quarters”. In the single-camp interpretation of this passage, Scipio must have crossed to the enemy side regardless of whether the camp was on the left or right bank. However, the narrative goes on to say that Hannibal did not cross the river to pursue them; thus, as previously, Scipio was placing the river between him and Hannibal. Following the thread of the previous narrative, Scipio must still have been in his camp at Ripa Alta. Some survivors managed to make their way upriver on the same side as the battle to Scipio’s camp. Scipio broke camp at night, crossed the river and reached Placentia on the right bank, past Sempronius’ now abandoned camp, or perhaps picking up the garrison left there along with additional survivors. He still had an army of such magnitude that it could not seek supplies in the same city as Sempronius’.

For a time, the Romans were spared attacks by the Carthaginians, as the latter were now suffering from exposure. A cold snap had set in and the precipitation had turned from rain to snow and ice. All the elephants but one (or several in Polybius) died along with “many men and horses”. When the news arrived at Rome that both consuls had been defeated at Ticinus and Trebbia, the population panicked, expecting to see Hannibal at the gates. In fact, the defeats were not the catastrophe they believed. Some 2.5 and more legions escaped from the battlefield, 3 more under Scipio never participated, while 2 more were in Spain; in all, the Senate still had 7.5 legions healthy and in good winter quarters.

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