In December 218 BC, soon after crossing the Alps into Italy, Hannibal destroyed a Roman army at the Trebia river. He drew the cold and hungry Romans across the freezing water at dawn, then sprang a hidden ambush on their rear; it was his first great victory of the Second Punic War.
The Battle of the Trebia was Hannibal's first great victory on Italian soil, and a brutal lesson in how he fought. Fresh from his crossing of the Alps, he met a Roman army on a freezing December day and destroyed it through patience, cunning and a well-hidden trap. This is how it happened.
Hannibal in Italy
In the autumn of 218 BC Hannibal completed his astonishing crossing of the Alps and descended into the plains of northern Italy, his army reduced but intact and swelling with Gaulish allies eager to strike at Rome. In a first clash of cavalry at the Ticinus river1 he got the better of the consul Publius Cornelius Scipio, who was wounded, and the Romans fell back.
The other consul, Tiberius Sempronius Longus, hurried north with his own army and took command of the combined force. Eager for a victory and contemptuous of the invader, he was exactly the opponent Hannibal wanted.
The trap on the Trebia
Hannibal chose his ground on the far bank of the Trebia and prepared it with care. He hid his brother Mago with a picked force2 of cavalry and infantry in a watercourse on the Roman flank, ready to strike the enemy rear once the battle was joined. Then, on a bitter December morning, he sent his light cavalry to harass the Roman camp and provoke a response.
Sempronius took the bait. He ordered his men out before they had eaten2 and sent them wading through the icy, chest-high river in pursuit2. By the time they formed up on the far bank they were cold, wet and exhausted, while Hannibal's troops had eaten, warmed themselves at fires and oiled their bodies against the cold2.
The battle
On the field Hannibal's stronger cavalry quickly drove the Roman horse from the wings, exposing the flanks of the legions, while his skirmishers and war elephants added to the confusion. As the Romans pressed forward against the Carthaginian centre, Mago's hidden force burst from cover and fell on their rear.
Caught front and back, the Roman army broke apart. A solid block of perhaps ten thousand men2 in the centre cut straight through the Carthaginian line and escaped to the safety of Placentia3, but the rest of the army was ridden down or drowned in the river. It was a near-total disaster for Rome.
Aftermath
The Trebia confirmed what the Alps had only hinted at: that Hannibal was a commander of the first rank, and that Rome faced a mortal threat on its own soil. The Gauls of northern Italy, who had hung back4 to see how the war would go, now flocked to his banner in numbers.
Rome, shaken but far from beaten, raised fresh armies for the next year. Its leaders still believed that a bold consul and superior numbers would be enough to crush the invader. They were wrong.
Toward Trasimene
In the spring of 217 BC Hannibal crossed the Apennines and the flooded marshes of Etruria, losing an eye to infection on the way2, and marched to provoke the new consul Gaius Flaminius. The result was an even greater catastrophe for Rome at Lake Trasimene, and then, a year later, the worst day in Roman military history at Cannae.