From this sketch of the trade of the Arabians from the earliest period, we may conclude, in the first place, that when navigation was in its infancy, it was confined, or almost entirely so, to a land trade carried on by caravans; and that Petra was the centre to which these caravans tended from the east and the south, bringing with them from the former the commodities of India, and from the latter the commodities of the more fertile part of Arabia. From Petra, all these goods were again transported by land to the shores of the Mediterranean and to Egypt. In the second place, when navigation became more commonly known and practised, (and there is good reason to believe that it was known and practised among the Arabians, especially those near the Persian Gulf, at a very early period,) a portion of the Indian commodities, which before had been carried by land to Petra were brought by sea to Sabaea. It appears that in the age of Agatharcides, the monopoly of the trade between India and Europe by this route was wholly possessed by the Sabeans; that, in order to evade the effects of this monopoly, the Greeks of Egypt found their way to Aden and Hadraumaut, in Arabia, and to Mosullon on the coast of Africa. Here they met with other Arabians, who at this time also traded to India, and sold them Indian goods at a cheaper rate. And, lastly, we have seen that these ports on the southern coast of Arabia, and on the coast of Africa, were frequented by the merchants of Egypt, till, by the discovery of the monsoon, their ships were enabled to sail directly to India. It is undoubtedly true that before this discovery, single ships occasionally reached India by adhering to the coast all the way, but the direct communication was very rare. After the nature of the monsoon was thoroughly understood, and it was ascertained that complete dependence could be placed on its steadiness and regularity, and that by its change, the ships could be brought as safely and quickly back from India, as they had reached it, the ancients, who at first only ventured to the mouth of the Indus, gradually made their way down the western coast of the Indian peninsula. The Periplus of the Erythrean Sea, a work which has been frequently referred to, is rich in materials to illustrate the geographical knowledge and the commercial enterprize of the ancients in the part of the world to which it relates. We have already assigned its date to the age of Nero. Our limits will prevent us from giving a full account of this work; we shall therefore, in the first place, give a short abstract of the geographical knowledge which it displays, and in the next place, illustrate from it, the nature of the commerce carried on, on the Red Sea, the adjacent coasts of Africa and Arabia, and the ports of India, which are noticed in it.