The military situation which finally resulted in the battle of the Metaurus and the triumph of Rome may be summed up as follows: To overthrow Rome it was necessary to attack her in Italy at the heart of her power, and shatter the strongly linked confederacy of which she was the head. This was the objective. To reach it, the Carthaginians needed a solid base of operations and a secure line of communications. The former was established in Spain by the genius of the great Barca family; the latter was never achieved. There were two lines possible,--the one direct by sea, the other circuitous through Gaul. The first was blocked by the Roman sea power, the second imperilled and finally intercepted through the occupation of northern Spain by the Roman army. This occupation was made possible through the control of the sea, which the Carthaginians never endangered. With respect to Hannibal and his base, therefore, Rome occupied two central positions, Rome itself and northern Spain, joined by an easy interior line of communications, the sea; by which mutual support was continually given. Had the Mediterranean been a level desert of land, in which the Romans held strong mountain ranges in Corsica and Sardinia, fortified posts at Tarragona, Lilybæum, and Messina, the Italian coast-line nearly to Genoa, and allied fortresses in Marseilles and other points; had they also possessed an armed force capable by its character of traversing that desert at will, but in which their opponents were very inferior and therefore compelled to a great circuit in order to concentrate their troops, the military situation would have been at once recognized, and no words would have been too strong to express the value and effect of that peculiar force. It would have been perceived, also, that the enemy's force of the same kind might, however inferior in strength, make an inroad, or raid, upon the territory thus held, might burn a village or waste a few miles of borderland, might even cut off a convoy at times, without, in a military sense, endangering the communications. Such predatory operations have been carried on in all ages by the weaker maritime belligerent, but they by no means warrant the inference, irreconcilable with the known facts, "that neither Rome nor Carthage could be said to have undisputed mastery of the sea," because "Roman fleets sometimes visited the coasts of Africa, and Carthaginian fleets in the same way appeared off the coast of Italy." In the case under consideration, the navy played the part of such a force upon the supposed desert; but as it acts on an element strange to most writers, as its members have been from time immemorial a strange race apart, without prophets of their own, neither themselves nor their calling understood, its immense determining influence upon the history of that era, and consequently upon the history of the world, has been overlooked. If the preceding argument is sound, it is as defective to omit sea power from the list of