Around the time the meteor fell, a young Greek tourist was traveling up the Nile River in Egypt. Armed with the latest theories and a boundless curiosity, he stopped to question Egyptian priests, the repositories of ageless wisdom: What was the cause of the Nile floods? Late each summer the river rose, running over its banks and bringing rich silt to restore the fertility of the land. But where did the water come from? To the south lay the Sahara Desert with its dry wasteland. No rain fell on Egypt in the summer. How then could the annual floods be accounted for?
The young man was Herodotus, destined to become known as the Father of History. A native of Halicarnassus in Ionia, he was on his Grand Tour to see the wonders of the world, to meet the peoples of the East, and to bring back the treasures of the Orient—treasures of knowledge about kingdoms and lands, the res gestae of kings and emperors. “Concerning the nature (phusis) of the river,” he reported, “I was not able to get any information either from the priests or from anybody else.”[19] No doubt they told him about the Nile god, but he did not take that kind of explanation seriously. He wanted to know about phusis, about the nature of the river, not some alleged supernatural influence.
Frustrated by the superstition of his informants, Herodotus tried out the theories he had brought with him. According to one, the “etesian” or annual winds that blew strongly off the Mediterranean Sea pushed against the Nile as the river flowed towards the sea, causing the river to back up and flood. The etesian winds blew in the late summer, around the time of the floods. But, objects Herodotus, some years the winds fail to blow, yet the Nile floods anyway. If the winds were the cause they should make all rivers in the region flood, but they do not have summer floods.
Second, some thinkers had suggested that the currents of Ocean, the stream that flows around the outer rim of the earth’s disk, feed into the Nile from an inlet in southern Africa, causing the river to flood. Hogwash, said Herodotus: there’s no such thing as Ocean. That was invented by Homer or some ignorant poet. Even if Anaximander put the mythical body of water called Ocean on his map, it was no more than a fiction.
Third, some had said that the floods were caused by melting snow. Herodotus saved his greatest scorn for this theory. The land south of Egypt was uniformly hot and dry; how could it collect snow? “The third approach,” said Herodotus, “which is by far the most plausible-sounding, is in fact the most wrong-headed. For it too is mistaken, claiming that the Nile, which flows in Africa through the middle of Ethiopia, and ends up in Egypt, originates from melted snow. Now how could it flow from snow, going from the hottest places to places most of which are cooler?”[20]
Herodotus did not tell us who developed these theories, but other ancient sources provide the names to go with them: the theory of the etesian winds comes from Thales; the theory of Ocean streams comes from Hecataeus of Miletus, a travel writer; and the snow theory comes from Anaxagoras, our prescient genius. Having refuted the three extant theories, Herodotus went on to propose his own, rather complicated but equally naturalistic, account of the floods.[21]
Pursuing his quest, Herodotus traveled on, searching for the sources of the Nile all the way to Elephantine. The goal he sought lay thousands of kilometers away, far beyond the pale of the Persian Empire which then controlled Egypt, and far beyond the limits of the civilized world he knew. The sources of the Nile, unfortunately, would not be discovered in central Africa until the nineteenth century AD, nor the reason for the river’s floods. Snows do not cause the floods, though the river is in fact fed by melting snow from lofty mountains in East Africa. Monsoon rains originating from the Indian Ocean and falling on the Ethiopian highlands are the real source of the flooding.[22] But the amazing thing was that a fifth-century Greek tourist was asking scientific questions that would still drive research twenty-four centuries later.
Perhaps a half century before Herodotus, a sailor from the western Greek colony Massalia (which the Romans later called Massilia, the French still later Marseilles) made a rare voyage into the Atlantic Ocean and found a place that he seems to have taken as the other end of the Nile, complete with palm trees and crocodiles. He observed that the river flowed violently into the sea when the etesian winds were blowing. He had perhaps reached the Senegal River in northwest Africa.[23]
Already in the late sixth and early fifth centuries BC, Greek travelers sailing to exotic lands were testing their observations against philosophical theories. Euthymenes and Herodotus were not philosophers, but curious travelers who had imbibed the daring new explanations of the world and then tried extending a knowledge of nature to the farthest corners of the world.
[19].Herodotus Histories 2.19.
[20].Herodotus Histories 2.19-22; quote from ch. 22.
[21].See Graham 2003d.
[22]. See Bonneau 1964.
[23].Seneca Natural Questions 4A.2.22. See Jacoby 1909; Cary and Warmington 1929.