But notwithstanding the authority of Caesar, Pliny, Solinus, and Lucan, who mention only these leathern vessels, and that the poet Avienus, who lived in the fourth century, expressly states, that even in his time the Britons had no ships made of timber, but only boats covered with leather or hides; there are circumstances which must convince us that they did possess larger, stronger, and more powerful ships. Caesar informs us, that the Britons often assisted the Gauls, both by land and sea; and we have seen that they sent assistance to the Vanni, in their sea-fight against Caesar; but it is not to be supposed that their leathern boats, small and weak as they were, could have been of any material advantage in an engagement with the Roman ships. Besides, the Britons, who inhabited the coast opposite to Gaul, carried on, as we have remarked, a considerable and regular trade with the Vanni; it is, therefore, reasonable to presume, that they would learn from this tribe, the art of building ships like theirs, which were so well fitted for these seas, as well as for war, that Caesar built vessels after their model, when he formed the determination of opposing them by sea. The Britons, however, certainly did not themselves engage much in the traffic with Gaul, and therefore could not require many vessels of either description for this purpose. From the earliest period, of which we have any record, till long after the invasion by Caesar, the commodities of Britain seem to have been exported by foreign ships, and the commodities given in exchange brought by these. In our account of the commerce of the Phoenicians, their trade to Britain for tin has been described. Pliny, in his chapter on inventions and discoveries, states that this metal was first brought from the Cassiterides by Midacritus, but at what period, or of what nation he was, he does not inform us. This trade was so lucrative, that a participation in it was eagerly sought by all the commercial nations of the Mediterranean, and even by the Romans, who, as we have seen, were not at this period, much given to commerce. This is evident, by the well known fact, of one of their vessels endeavouring to follow the course of a Phoenician or Carthaginian vessel, in her voyage to Britain. The Greeks of Marseilles, according to Polybius, first followed, successfully, the course of the Phoenicians, and, about 200 years before Christ, began to share with them in the tin trade. Whether, at this period, they procured it exclusively by direct trade with Britain, is not known; but afterwards, as we have already mentioned, Marseilles became one of the principal depots for this metal, which was conveyed to it through Gaul, and exported thence by sea.