 Complete the following phrase:  In 219BC Hannibal besieged, captured and sacked the pro-Roman city of Saguntum, prompting a Roman declaration of war on Carthage in spring 218BC. That year, Hannibal surprised the Romans by marching his army overland from Iberia, through Gaul and over the Alps to Cisalpine Gaul modern northern Italy. Reinforced by Gallic allies, he obtained crushing victories over the Romans at the battles of Trebia 218 and 