Hannibal's passage over the Alps is one of the most celebrated achievements of any military force in ancient warfare. Hannibal successfully crossed the Alps, despite numerous obstacles such as harsh climate and terrain, the guerrilla tactics of the native tribes, and the challenge of commanding an army diverse in race and language.
Hannibal's forces moved through the Po Valley and were engaged in a small confrontation at Ticinus. Here, Hannibal forced the Romans, by virtue of his superior cavalry, to evacuate the plain of Lombardy. While the victory was minor, it encouraged the Gauls and Ligurians to join the Carthaginian cause, whose troops bolstered his army back to 40,000 men. Scipio was severely injured and retreated across the river Trebia to camp at Placentia with his army intact.
Hannibal then captured Clastidium, from which he drew large amounts of rations for his men. But this gain was not without its loss, as Sempronius avoided Hannibal's watchfulness, slipped around his flank, and joined his colleague in his camp near the Trebbia River near Placentia. There, in December of the same year, Hannibal had an opportunity to show his superior military skill at Trebia; after wearing down the excellent Roman infantry he cut it to pieces by a surprise attack from an ambush in the flank.
After the Battle of Lake Trasimenus Hannibal had now disposed of the only field force which could check his advance upon Rome, but, realizing that without siege engines he could not hope to take the capital, he preferred to exploit his victory by passing into central and southern Italy and encouraging a general revolt against the sovereign power. After Lake Trasimeno, Hannibal stated, I have not come to fight Italians, but on behalf of the Italians against Rome.
Due to his brilliant tactics, Hannibal, with much inferior numbers, managed to surround and destroy all but a small remainder of a Roman army led by Varro. Depending upon the source, it is estimated that 50,000-70,000 Romans were killed or captured at Cannae. Among the dead were the Roman consul Lucius Aemilius Paullus, as well two consuls for the preceding year, two quaestors, twenty-nine out of the forty-eight military tribunes and an additional eighty senators (at a time when the Roman Senate comprised no more than 300 men, this constituted 25%30% of the governing body). This makes the Battle of Cannae one of the most catastrophic defeats in the history of Ancient Rome, and one of the bloodiest battles in all of human history (in terms of the number of lives lost within a single