tribes, who were finally defeated in 222BC. In 218BC the Romans pushed even further north, establishing two new towns, or "colonies", on the Po and appropriating large areas of the best land. Most of the Gauls simmered with resentment at this intrusion. The major Gallic tribes in Cisalpine Gaul attacked the Roman colonies there, causing the Romans to flee to their previously established colony of Mutina (modern Modena), where they were besieged. A Roman relief army broke through the siege, but was then ambushed and itself besieged in Tannetum. It was the long-standing Roman procedure to elect two men each year, known as consuls, to each lead an army. In 218 BC the Romans raised an army to campaign in Iberia under the consul Publius Scipio, who was accompanied by his brother Gnaeus. The Roman Senate detached one Roman and one allied legion from the force intended for Iberia to reinforce the Roman position in northern Italy. The Scipios had to raise fresh troops to replace these and thus could not set out for Iberia until September. At the same time another Roman army in Sicily under the consul Sempronius Longus was preparing for an invasion of Carthaginian Africa. Carthage invades Italy Meanwhile, Hannibal assembled a Carthaginian army in New Carthage (modern Cartagena) over the winter, marching north in May 218 BC. He entered Gaul to the east of the Pyrenees, then took an inland route to avoid the Roman allies along the coast. Hannibal left his brother Hasdrubal Barca in charge of Carthaginian interests in Iberia. The Roman fleet carrying the Scipio brothers' army landed at Rome's ally Massalia (modern Marseille) at the mouth of the Rhone in September, at about the same time as Hannibal was fighting his way across the river against a force of local Gauls at the battle of Rhone Crossing. A Roman cavalry patrol scattered a force of Carthaginian cavalry, but Hannibal's main army evaded the Romans and Gnaeus Scipio continued to Iberia with the Roman force; Publius returned to northern Italy to coordinate the immediate Roman response there. The Carthaginians crossed the Alps with 38,000 infantry and 8,000 cavalry in October 218 BC, surmounting the difficulties of climate, terrain and the guerrilla tactics of the native tribes. Hannibal arrived with 20,000 infantry, 6,000 cavalry and 37 elephants in what is now Piedmont, northern Italy. The Romans had already withdrawn to their winter quarters