The other natural wonder of Egypt was the annual rising of the Nile. About midsummer, the peasantry who lived along the banks would find the river gradually beginning to rise. The stream became more turbid, too, as the bosom of the waters swelled. No cause for this mysterious increase appeared, as the sky remained as blue and serene as before, and the sun, then nearly vertical, continued to shine with even more than its wonted splendor. The inhabitants however, felt no surprise, and asked for no explanation of the phenomenon. It was the common course of nature at that season. They had all witnessed it, year after year, from childhood. They, of course, looked for it when the proper month came round, and, though they would have been amazed if the annual flood had failed, they thought nothing extraordinary of its coming. When the swelling of the waters and the gradual filling of the channels and low grounds in the neighborhood of the river warned the people that the flood was at hand, they all engaged busily in the work of completing their preparations. The harvests were all gathered from the fields, and the vast stores of fruit and corn which they yielded were piled in roofless granaries, built on every elevated spot of ground, where they would be safe from the approaching inundation. The rise of the water was very gradual and slow. Streams began to flow in all directions over the land. Ponds and lakes, growing every day more and more extended, spread mysteriously over the surface of the meadows; and all the time while this deluge of water was rising to submerge the land, the air continued dry, the sun was sultry, and the sky was without a cloud. As the flood continued to rise, the proportion of land and water, and the conformation of the irregular and temporary shores which separated them, were changed continually, from day to day. The inhabitants assembled in their villages, which were built on rising grounds, some natural, others artificially formed. The waters rose more and more, until only these crowded islands appeared above its surface--when, at length, the valley presented to the view the spectacle of a vast expanse of water, calm as a summer's sea, brilliant with the reflected rays of a tropical sun, and canopied by a sky, which, displaying its spotless blue by day and its countless stars at night, was always cloudless and serene. The inundation was at its height in October. After that period the waters gradually subsided, leaving a slimy and very fertilizing deposit all over the lands which they had covered. Though the inhabitants themselves, who had been accustomed to this overflow from infancy, felt no wonder or curiosity about its cause, the philosophers of the day, and travelers from other countries who visited Egypt, made many attempts to seek an explanation of the phenomenon. They had three theories on the subject, which Herodotus mentions and discusses.