BC a Carthaginian army under Hannibal besieged, captured and sacked Saguntum. In spring 218 BC Rome declared war on Carthage, starting the Second Punic War. Carthage invades Italy In 218 BC the Romans raised an army to campaign in Iberia under the brothers Gnaeus and Publius Scipio. The major Gallic tribes in Cisalpine Gaul (modern northern Italy) attacked the Romans, capturing several towns and ambushing a Roman army. The Roman Senate detached one Roman and one allied legion from the force intended for Iberia to send to the region. The Scipios had to raise fresh troops to replace these and thus could not set out for Iberia until September. Meanwhile, Hannibal assembled a Carthaginian army in New Carthage (modern Cartagena) and entered Gaul, taking 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 River Rhone at about the same time as Hannibal was fighting his way across the river against a force of local Allobroges at the Battle of Rhone Crossing. Hannibal evaded the Romans and Gnaeus Scipio continued to Iberia with the Roman army; Publius returned to Rome. The Carthaginians crossed the Alps early in 217 BC, taking the Romans by surprise and causing them to cancel their main campaign planned for the year, an invasion of Africa. Rome invades Iberia Gnaeus Scipio continued on from Massala to Iberia, landing his army of four legions, two Roman and two allied —approximately 25,000 men— in the autumn of 218 BC at Cissa and winning support among the local tribes. The Carthaginian commander in the area, Hanno, refused to wait for Carthaginian reinforcements under Hasdrubal, attacked Scipio at the Battle of Cissa in late 218 BC and was defeated. In 217 BC, the Carthaginians moved to engage the combined Roman and Massalian fleet at the Battle of Ebro River, in which Hasdrubal launched a joint operation, advancing into the Roman controlled area in close cooperation with a fleet of 40 Carthaginian and Iberian quinqueremes. The naval component was defeated by 55 Roman and Massalian vessels at the Battle of Ebro River, with 29 Carthaginian ships were lost. In the aftermath the Carthaginian forces retreated, but the Romans remained confined to the area between the Ebro and