Alexander’s expedition into India was no less an intelligent exploration than a successful invasion, and the western world is more indebted than is generally understood to the original genius, conspicuous foresight, political wisdom, and indefatigable exertions of that remarkable man. It was from the memoirs of his officers that Europe derived its first authentic information concerning the climate, soil, inhabitants and productions of India, and amongst the last not the least beneficial to man was cotton. Although Scylax of Caryandra, an emissary of Darius Hydaspes, had descended the Indus to the sea about a hundred and eighty years previously (B.C. 509), other nations had derived no benefit from his investigations. But his report of the fertility, high cultivation, and opulence of the country he had passed through inflamed his master’s greed, and made Darius impatient to become possessor of a territory so valuable. This he soon accomplished, and though his conquests seem not to have extended beyond the districts watered by the Indus, he levied a tribute from it which equalled in amount one-third of the whole revenue of the Persian Monarchy. Until Alexander became master of Persia no commercial intercourse seems to have been carried on by sea between that country and India. The ancient rulers of Persia, induced by a peculiar precept of their religion which enjoined them to guard with the utmost care against the defilement of any of the “elements,” and also by a fear of foreign invasion, obstructed by artificial works near their mouths the navigation of the great rivers which gave access to the interior of the country. As their subjects, however, were no less desirous than the people around them of possessing the valuable productions and elegant manufactures of India, these latter were conveyed to all parts of their dominions by land carriage. The goods destined for the northern provinces were borne on camels from the banks of the Indus to those of the Oxus, down the stream of which they were carried to the Caspian Sea, and distributed, partly by land and partly by navigable rivers, through the different countries bounded on the one hand by the Caspian, and on the other by the Euxine, or Black Sea; whilst those of India intended for the southern and interior districts were transported by land from the Caspian Gates to some of the great rivers, by which they were dispersed through every part of the country. This was the ancient mode of intercourse with India, whilst the Persian Empire was governed by its native princes; and, as Robertson says, “it has been observed in every age that when any branch of commerce has got into a certain channel, although it may not be the best or most convenient one, it requires long time and persistent efforts to give it a different direction.”[38] [38] Robertson’s ‘Historical Disquisition Concerning India.’