crossed the desert for many days, and were at last taken captive by black men of small stature, who carried them to a city on the banks of this river, whence they were subsequently allowed to return. It has been eagerly discussed what truth underlies this story, and whether the river was the Niger in its upper course; but at best the account added little to the knowledge of distant Africa. The idea of a pygmy people dwelling towards the southern shore of the ocean is older than the Iliad in which it is found (III, 3). Herodotus’s conception of the shape of Africa did not carry its southward extension much beyond the latitude of Cape Guardafui. He discarded the popular conception of the round earth, regarding it as longer from east to west than from north to south. The philosopher Democritus of Abdera (born _c._ 470–450) exhibited the same conception in a map which he constructed. An important episode in the progress of a more accurate knowledge of the world of the Greeks was the Retreat of the Ten Thousand under Xenophon in 401–400 B.C. The younger Cyrus had made a great expedition from Sardis, in western Asia Minor, eastwards through the Cilician Gates to the Euphrates, and along the course of that river to the neighbourhood of Babylon. He was accompanied by a band of Greek mercenaries, who, after his defeat at Cunaxa, began the retreat of which Xenophon left a graphic account, containing what must have been to the Greeks much new information concerning the region from the junction of the Tigris and Euphrates northwards past Lake Van and through the mountains of Armenia, north and west to the shores of the Black Sea at Trapezus (Trebizond), and along the south coast of the Black Sea, partly by sea and partly by water, to Byzantium. Xenophon’s story is an illustration of the well-known fact that war is one of the chief means of promoting geographical knowledge. This will appear more clearly in the next important episode in the story of exploration--the campaign of Alexander the Great.