The Battle of Trebia was the first of Hannibal
's great victories in Italy
. The battle took place in the winter of 218/217 B.C., which was a particularly snowy winter. Hannibal was facing Tiberius Sempronius Longus
, an impetuous Roman
commander, who had 36000 infantry
and 4000 cavalry to Hannibal's 29000 infantry and 11000 cavalry
, Hannibal also had his 37 elephants that he led over the Alps
Hannibal split off a force of 1000 infantry and 1000 cavalry under the command of his younger brother, Mago, and sent them to hide in the stream beds along the River Trebia (Modern: Trebbia). He then sent a force of Numidian cavalry to harass the Roman camp while his men had breakfast and oiled themselves against the cold. The impetuous Roman general led his men after the numidians crossing the icy Trebia, leaving him with a force comprised of cold and hungry men. Hannibal set up a screen of light infantry a short distance from the river, with his infantry behind them and his elephants and cavalry on the flanks. The Roman and Carthaginian light infantries clashed, the Carthaginians coming out on top forcing the Roman light infantry back to the Roman battle line. The main Roman body advanced, however the Carthaginian wings and light infantry clashed with and ran off the Roman cavalry wings. This meant that when the main blocks of infantry clashed the Romans were already being harassed on the flanks by elephants and light infantry, while the Carthaginian cavalry chased down the fleeing Roman cavalry. The elephants succeeded in routing the Roman Gauls, however they in turn were forced to back off by the Roman light infantry. The main infantry blocks were locked in bitter hand to hand combat, and the Carthaginian centre was beginning to weaken as this was primarily made up of newly recruited Gauls. However the battle was decided when Mago and his force broke cover attacking the Roman rear. The Roman flanks broke and fled across the river many drowning or being cut down, however the Roman centre held together and led by Sempronius, they reached Placentia. The Roman death toll is estimated to be close to 20000 men while Hannibal's was considerably lower, with most of his losses being taken by the Gauls.
This battle was decided to a large extent on the quality of Hannibal's planning, he knew his opponent was impetuous and used this to his advantage. Notably this was the only major battle where Hannibal got to use the elephants he brought over the Alps, since many died either from wounds or the cold after the battle.