|Crossing the Rhône|
Along the way, Hannibal recruited reinforcements from the warlike Celtic tribes who hated Rome. (see Gaul before the Romans)
The Romans, shortly before they heard of this, had decided on war. Hannibal's offensive move meant that they had to mobilise quickly to meet the threat.
Polybius states that Hannibal crossed the Rhône while the river was still in one stream at a distance of four days' march from the sea.
Fourques, opposite Arles, is thought to be a likely place, but he may have made a crossing north of the confluence of the Isère and the Rhône. Hannibal used coracles and boats locally commandeered; for the elephants he made jetties out into the river and floated the elephants from these on earth-covered rafts. Horses were embarked on large boats or made to swim.
During this operation hostile Gauls appeared on the opposite bank, and Hannibal dispatched a force under Hanno to cross farther upstream and attack them in the rear.
Meanwhile, two Roman armies had been levied: one, commanded by the consul Publius Cornelius Scipio, was intended to oppose Hannibal in Spain; and a second, under the consul Titus Sempronius, was designed for the invasion of Africa. The departure of Scipio was delayed by a revolt of the Boian and Insubrian Gauls, against whom was sent the army which had been intended for the invasion of Spain, under the command of one of the praetors, Lucius Manlius to defend the Po against possible Gaulish uprisings. Scipio was therefore obliged to remain in Rome until a new army could be raised.
When the forces were ready, the Roman army commanded by Consul Publius Cornelius Scipio and his brother Gnaeus Cornelius Scipio sailed from Italy to to Massilia (Marseille). As Scipio moved northward along the right bank of the Rhône, he learned that Hannibal had already crossed the river and was marching northward on the left bank.
The main Roman army commanded by the other Consul, Titus Sempronius, was preparing in Sicily to invade Africa. Learning of Hannibal's movements the Romans brought this army from Sicily by sea to the Po to join in the defence against Hannibal.
After crossing the Rhone, Hannibal avoided conflict with the Roman commander Publius Cornelius Scipio by turning northward up the Rhone River valley.
Realising that Hannibal probably planned to cross the Alps, Scipio sent his brother with the troops on to Spain but returned himself to northern Italy to await Hannibal.
After crossing and receiving friendly Gallic leaders headed by the northern Italian Boii, whose superior knowledge of the Alpine passes must have been of the greatest value to Hannibal's plans, the Carthaginians crossed the Durance River (or more probably an ancient branch of it that flowed into the Rhône near Avignon) and passed into an area called "the island," the identification of which is the key to Hannibal's subsequent movements on land.
According to Polybius, it was a fertile, densely populated triangle bounded by hills, by the Rhône, and by a river that is probably either the Aygues or the Isère. On the "island" a civil war was being fought between two brothers (of what tribe it is not clear). Brancus, the elder, in return for Hannibal's help, provided supplies for the Carthaginian army, which were sorely needed, as the army had marched about 750 miles in four months from Carthago Nova.