But, beyond numerous commercial advantages, the Macedonian campaigns opened a large and beautiful portion of the earth to the influence of a highly-gifted race, who courted the society of the most learned men of the countries they conquered. Hence the geographical knowledge of the Greeks was more than doubled in the course of a very few years by the extraordinary and enlightened conquests of their chief. While the comparison of notes between the geometricians, naturalists, and astronomers of two of the most learned nations of ancient times proved of immense benefit to mankind, we cannot doubt that the scientific knowledge of the Greeks, when brought to bear upon the practical experience of the Hindus with regard to the prevailing winds, mainly induced Nearchus to start without fear on his celebrated voyage, and, at the same time, encouraged the merchants of Europe to seek out new means of communication with a country producing in such abundance the articles they prized so highly. [Sidenote: His march into India.] The expedition through the northern portions of India, and the voyage from the Indus to the Euphrates, if not the greatest of the exploits of Alexander, were certainly, in many ways, the most important up to that time in the history of commerce and navigation. Arrian, whom we have had so often the pleasure of quoting, has preserved copious extracts from the journal of Nearchus, and the information thus obtained has been thoroughly investigated by Dr. Robertson, in his “Disquisition on the Knowledge the Ancients had of India”; by Heeren in his “Asiatic Nations”; and most fully of all by Dr. Vincent in his “Commerce and Navigation of the Ancients in the Indian Ocean.” With a view to secure the commerce Tyre had so long and so successfully carried on with India, Alexander, early in his career, as has been shown, established the great Egyptian port which still bears his name; and other events soon gave him the opportunity of obtaining the sovereignty of those regions that supplied the rest of the world with so many precious commodities. After his victory over the Persians, the pursuit of Darius led him across Asia, from the Caspian Sea to Maracanda (Samarcand), and during this adventurous march he naturally learnt many things, not only of the tribes through whom he passed, but also of India itself, with which those tribes had much commercial intercourse. Decisive and prompt in his resolutions, he accordingly set out from Bactra (Balkh), crossed the great chain of mountains that constitutes the north-western boundary of India, and, passing the Indus, marched on towards the Ganges and the rich provinces of the south-east, now comprehended under the general name of Hindustan. [Sidenote: Preparations for the voyage down the Indus.]