Herodotus trusted principally or entirely to the information he received, with respect to the interior of Africa and the north of Europe, and Asia to the east of Persia. While he was in Egypt he seems to have been particularly inquisitive and interested respecting the caravans which travelled into the interior of Africa; and regarding their equipment, route, destination, and object, he has collected a deal of curious and instructive information. On the authority of Etearchus, king of the Ammonians, he relates a journey into the interior of Africa, undertaken by five inhabitants of the country near the Gulf of Libya; and, in this journey, there is good reason to believe that the river Niger is accurately described, at least as far as regards the direction of its course. It is evident from the introduction to his third book that the Greek merchants of his time were eminently distinguished for their courage, industry, and abilities; that in pursuit of commercial advantages they visited very remote and barbarous countries in the north-eastern parts of Europe, and the adjacent parts of Asia; and that the Scythians permitted the Greek merchants of the Euxine to penetrate farther to the east and north "than we can trace their progress by the light of modern information." To them Herodotus was much indebted for the geographical knowledge which he displays of those parts of the world; and it is by no means improbable that the spirit of commercial enterprize which invited the Greek merchants on the Euxine to penetrate among the barbarous nations of the north-east, also led them far to the east and south-east; and that from them, as well as from his personal enquiries, while at Babylon and Susa, Herodotus derived much of the information with which he has favoured us respecting the country on the Indus, and the borders of Cashmere and Arabia. Having thus pointed out the sources from which Herodotus derived his geographical knowledge, we shall now sketch the limits of that knowledge, as well as mention in what respects he yielded to the fabulous and absurd notions of his contemporaries.