There was much curiosity among educated Greeks about the Nile River in Egypt. What was its source and its upper course? Why did it flood yearly? Geographers had tried for centuries to answer these questions with varying degrees of success; the mysterious Nile had come to represent a mythic geographical riddle. While in Indian in 324 B.C.E. Alexander the Great thought he had the answer. The historian Arrian tells the story:

Alexander fancied at this time that he had discovered the source of the Nile, his reasons being that he had on a previous occasion, seen crocodiles in the Indus, and in no other river except the Nile, and had also observed a kind of bean like the Egyptian bean growing on the banks of the Aescines, which, he was told, flowed into the Indus. His notion was that...