The war began with the Carthaginian general Hannibal 's conquest and destruction of the Roman - allied Iberian city of Saguntum in 219 BC, prompting a Roman declaration of war on Carthage in 218. Hannibal surprised the Romans by marching his army overland from Iberia to cross the Alps and invade Roman Italy, followed by his reinforcement by Gallic allies and crushing victories over Roman armies at Trebia in 218 and on the shores of Lake Trasimene in 217. Moving to southern Italy in 216, Hannibal at Cannae annihilated the largest army the Romans had ever assembled, killing or capturing more than 67,000 Roman soldiers. After the death or imprisonment of 130,000 Roman troops in two years, 40 % of Rome 's Italian allies defected to Carthage, giving her control over most of southern Italy. Macedon and Syracuse joined the Carthaginian side after Cannae and the conflict spread to Greece and Sicily. The Carthaginian navy was built up in the early years of the war, and from 215 -- 210 the Carthaginian army and navy launched amphibious assaults to capture Roman Sicily and Sardinia but were ultimately repulsed.
who was the skilled general who led his troops over the alps into rome during the second punic war
Carthaginian general Hannibal