On 21 December 218 BCE, the Battle of Trebia was fought between the Carthaginians under Hannibal Barca and the Romans under Sempronius Longus during the Second Punic War.
Why did it happen?
In 221 BCE, Hannibal Barca assumed command of Carthaginian forces in Spain and set about his plans for the invasion of Italy. In 219 BCE, Hannibal besieged the pro-Roman town of Saguntum, effectively declaring war on Rome. In June 218 BCE, Hannibal set out from Spain with a force comprised of 50,000 infantry, 9,000 cavalry and 37 war elephants to cross over the Alps into Italy. This was done to achieve surprise and bypass Roman garrisons stationed south of the Alps, in addition to the fact that the Romans had control of the sea. Although Hannibal’s forces were reduced to 26,000 men by the time he arrived in Italy, he managed to recruit Gallic warriors to his cause after defeating the Romans in a cavalry skirmish at the Ticinus River. A few weeks later in December, Hannibal faced a major Roman army under Sempronius Longus across the Trebia river.
Who was involved?
The Carthaginian army at Trebia comprised of 28,000 infantry, 10,000 cavalry and 37 war elephants. Hannibal’s plan was to send a force of Numidian cavalry to harass the Roman camp and lure the Roman army across the freezing Trebia river where it could be engaged in a set-piece battle. Hannibal’s main army would consist of heavy infantry in the centre, light infantry in the vanguard while the cavalry and war elephants would be arranged on the flanks. In addition, Mago Barca would be hidden nearby with 2,000 troops ready to attack the Roman army in the rear. The Roman army consisted of 36,000 infantry and 4,000 cavalry.
What happened?
At dawn on 21 December, Hannibal sent his Numidian cavalry to harass the Roman camp with missile fire before retreating across the Trebia River. This prompted Sempronius Longus to send his army across the river and arrange itself in three lines with cavalry on the wings. As the Roman infantry advanced, it forced the Carthaginian light infantry to withdraw behind the Carthaginian heavy infantry which then engaged the Roman infantry in hand-to-hand combat. At the same time, the Carthaginian cavalry and war elephants attacked the Roman cavalry and routed them before falling upon the flanks of the Roman infantry. Once this had happened, the order was given for Mago Barca to emerge from the nearby woods and attack the Romans in the rear, effectively surrounding them. While most of the Roman army was butchered, Sempronius Longus and 10,000 legionaries managed to hack their way through the Carthaginian army and escape to the nearby town of Piacenza. While Roman casualties numbered 30,000 killed, Carthaginian losses numbered about 5,000 men.
What changed as a result?
The Battle of Trebia was a victory for the Carthaginians. Not only did it open the rest of Italy to Hannibal, but it also demonstrated his tactical genius, particularly his trademark double envelopment manoeuvre, that would confound the Romans again at the Battle of Cannae. As Patrick N. Hunt analysed,
“Hannibal won his first Italian victory by careful strategy and thoughtful preparation against a Roman army that outnumbered him. He exploited Roman weaknesses in leadership. He also exploited weakness in Roman tactics, especially the outmatched Roman cavalry and Roman overdependence on slow infantry, as well as the use of raw legions. Hannibal used nature fully to his advantage. Having found a way to defeat Rome, he would use all of these strategies again (Hunt, 2017, p.97).
Following the battle, Hannibal lost all but one of his elephants to frostbite. In addition, after crossing the Arno Marshes during the march into Etruria, Hannibal contracted an eye infection that caused him to lose sight in one eye. Nevertheless, Trebia brought Gallic allies to his standard and would mark the beginning of his sixteen-year-long campaign against Rome.
Bibliography
Grant, R.G. 1001 Battles That Changed the Course of History. London, Cassell Illustrated, 2011.
Grant, R.G. Battle: A Visual Journey Through 5,000 Years of Combat. London, Dorling Kindersley, 2005.
Hunt, Patrick N. Hannibal. New York, Simon & Schuster Paperbacks, 2017.
Polybius. Histories. Translated by Evelyn S. Shuckburgh. New York, Macmillan, 1889.
Webb, Jonathan. “Battle of the Trebia, 218 BC.” The Art of Battle. Last revised 2009. http://www.theartofbattle.com/battle-of-the-trebia-218-bc/