218 BCE, c. December 20
The Second Punic War begins with the Carthaginian victory at the Battle of the Trebia in December 218 BCE. The battle was the first major engagement of the war, which was triggered by Hannibal's attack on the Roman-allied city of Saguntum in Spain. The battle was a crushing defeat for the Romans and a decisive victory for Hannibal, who led his forces across the Alps to invade Italy.