Alexander the Great (356–323 B.C.), King of Macedon, however, during the last few years of his life, made possible by his campaigns a greater extension of Greek geographical knowledge than had taken place almost since Homeric times. When he passed eastward through Mesopotamia, by Babylon, Susa, and Persepolis, and through Media to the southern shore of the Caspian Sea, he was in a region which, though an ancient cradle of civilization, had been till then only vaguely known to the Greeks. Beyond that he entered new country, peopled by Herodotus and others with dubious tribal names. He came almost into the heart of Central Asia, founding a city on the upper course of the Jaxartes. Passing southwards through Bactria and across formidable ranges of mountains such as the Hindu Kush, he struck the upper course of the Indus, made his way down to its delta, and would have proceeded right into the heart of India and followed the Ganges to its mouth but for his mutinous troops. He returned through the north of Baluchistan and Persia to Ecbatana, and so homeward. He also sent a member of his staff, Nearchus, by sea along the coast of Baluchistan and Persia, in order to define it and to ascertain the extent of the Persian Gulf. Dicæarchus of Messana, a pupil of Aristotle, who died early in the third century B.C., used the geographical results of Alexander’s expeditions, including the distances obtained by his bematists, or measurers by pacing. Dicæarchus wrote a topography of Greece, and also drew on a map a parallel or equator, for the first time, so far as is known, along the length of the Mediterranean and, with a distorted idea of their relative directions, along the Taurus and Himalayan ranges. Before his time, and probably contemporaneously with Alexander’s campaigns, Pytheas of Massilia (Marseilles) visited (practically discovered) Britain, and made mention of Thule, six days’ voyage north of it, having perhaps heard of the Orkneys and Shetlands. As these islands, however, are at no such great distance as is here suggested from the nearest point of Britain, the name of Thule has been variously taken to represent some part of Norway, the Faeröe, or Iceland: it certainly seems by some later writers to be applied to Scandinavia, and in literary usage came to signify the uttermost north. Pytheas also obtained an idea of the Baltic Sea, and is considered by some to have entered it; he is stated to have reached the River Tanais; but if that is to be considered as one of the north European rivers, and not the known Tanais of the Black Sea basin, its identity is doubtful. Pytheas was a trained astronomer; he was one of the first to calculate latitudes, and had that of Massilia nearly correct; he heard of the unbroken summer daylight and winter darkness of the far north, and he noted various features of geographical interest, such as the decrease in the number of different grain crops observed as he travelled northward.