When Rome demanded satisfaction of Carthage for this insult, and declared herself ready for war, the Carthaginians accepted the challenge, and the Second Punic War began in 218. CHAPTER XIV. THE SECOND PUNIC WAR.--FROM THE PASSAGE OF THE PYRENEES TO THE BATTLE OF CANNAE. (218-216.) In the spring of 218 Hannibal started from Carthago Nova to invade Italy. His army consisted of 90,000 infantry, 12,000 cavalry, and 37 elephants. His march to the Pyrenees occupied two months, owing to the opposition of the Spanish allies of Rome. Hannibal now sent back a part of his troops, retaining 50,000 infantry and 9,000 cavalry, all veterans. With these he crossed the mountains, and marched along the coast by Narbo (Narbonne) and Nemansus (Nimes), through the Celtic territory, with little opposition. The last of July found him on the banks of the Rhone, opposite Avenio (Avignon). The Romans were astonished at the rapidity of his movements. The Consuls of the year were SCIPIO and SEMPRONIUS. The former had been in Northern Italy, leisurely collecting forces to attack Hannibal in Spain; the latter was in Sicily, making preparations to invade Africa. Scipio set sail for Spain, touching at Massilia near the end of June. Learning there for the first time that Hannibal had already left Spain, he hoped to intercept him on the Rhone. The Celtic tribes of the neighborhood were won over to his side. Troops collected from these were stationed along the river, but Scipio's main army remained at Massilia. It was Hannibal's policy to cross the river before Scipio arrived with his troops. He obtained all the boats possible, and constructed numerous rafts to transport his main body of troops. A detachment of soldiers was sent up the river with orders to cross at the first available place, and, returning on the opposite bank, to surprise the Celtic forces in the rear. The plan succeeded. The Celts fled in confusion, and the road to the Alps was opened. Thus Scipio was outgeneralled in the very beginning. His course now should have been to return to Northern Italy with all his forces, and take every means to check Hannibal there. Instead, he sent most of his troops to Spain under his brother Gnaeus Scipio, and himself, with but a few men, set sail for Pisae.