18. The lower classes of the centuries were excused from serving in the army, except on dangerous emergencies; but they supplied sailors to the navy. We learn, from a document preserved by Polyb'ius, that the Romans were a naval power at a very early age. 19. This interesting record is the copy of a treaty concluded with the Carthaginians, in the year after the expulsion of the kings. It is not mentioned by the Roman historians, because it decisively establishes a fact which they studiously labour to conceal, that is, the weakness and decline of the Roman power during the two centuries that followed the abolition of royalty, when the power of the state was monopolized by a vile aristocracy. In this treaty Rome negociates for the cities of La'tium, as her dependencies, just as Carthage does for her subject colonies. But in the course of the following century, Rome lost her supremacy over the Latin cities, and being thus nearly excluded from the coast, her navy was ruined. 20. At the commencement of the first Punic war, the Romans once more began to prepare a fleet, and luckily obtained an excellent model in a Carthaginian ship that had been driven ashore in a storm. 21. The vessels used for war, were either long ships or banked galleys; the former were not much used in the Punic wars, the latter being found more convenient. The rowers of these sat on banks or benches, rising one above the other, like stairs; and from the number of these benches, the galleys derived their names; that which had three rows of benches was called a _trireme_; that which had four, a _quadrireme_; and that which had five, a _quinquireme_. Some vessels had turrets erected in them for soldiers and warlike engines; others had sharp prows covered with brass, for the purpose of dashing against and sinking their enemies. 22. The naval tactics of the ancients were very simple; the ships closed very early, and the battle became a contest between single vessels. It was on this account that the personal valour of the Romans proved more than a match for the naval skill of the Carthaginians, and enabled them to, add the empire of the sea to that of the land.