As Hannibal left no memoirs, the motives are unknown which determined him to the perilous and almost ruinous march through Gaul and across the Alps. It is certain, however, that his fleet on the coast of Spain was not strong enough to contend with that of Rome. Had it been, he might still have followed the road he actually did, for reasons that weighed with him; but had he gone by the sea, he would not have lost thirty-three thousand out of the sixty thousand veteran soldiers with whom he started. While Hannibal was making this dangerous march, the Romans were sending to Spain, under the two elder Scipios, one part of their fleet, carrying a consular army. This made the voyage without serious loss, and the army established itself successfully north of the Ebro, on Hannibal's line of communications. At the same time another squadron, with an army commanded by the other consul, was sent to Sicily. The two together numbered two hundred and twenty ships. On its station each met and defeated a Carthaginian squadron with an ease which may be inferred from the slight mention made of the actions, and which indicates the actual superiority of the Roman fleet. After the second year the war assumed the following shape: Hannibal, having entered Italy by the north, after a series of successes had passed southward around Rome and fixed himself in southern Italy, living off the country,--a condition which tended to alienate the people, and was especially precarious when in contact with the mighty political and military system of control which Rome had there established. It was therefore from the first urgently necessary that he should establish, between himself and some reliable base, that stream of supplies and reinforcements which in terms of modern war is called "communications." There were three friendly regions which might, each or all, serve as such a base,--Carthage itself, Macedonia, and Spain. With the first two, communication could be had only by sea. From Spain, where his firmest support was found, he could be reached by both land and sea, unless an enemy barred the passage; but the sea route was the shorter and easier. In the first years of the war, Rome, by her sea power, controlled absolutely the basin between Italy, Sicily, and Spain, known as the Tyrrhenian and Sardinian Seas. The sea-coast from the Ebro to the Tiber was mostly friendly to her. In the fourth year, after the battle of Cannæ, Syracuse forsook the Roman alliance, the revolt spread through Sicily, and Macedonia also entered into an offensive league with Hannibal. These changes extended the necessary operations of the Roman fleet, and taxed its strength. What disposition was made of it, and how did it thereafter influence the struggle?