The geography of the section comprising the nations where the earliest achievements have left permanent records, indicates a land extending from a territory east of the Tigris and Euphrates westward to the eastern shore of the Mediterranean and southward into Egypt. Doubtless, this region was one much traversed by tribes of various languages and cultures. Emerging from the Stone Age, we find the civilization ranging from northern Africa and skirting Arabia through Palestine {153} and Assyria down into the valley of the Tigris and the Euphrates. Doubtless, the civilization that existed in this region was more or less closely related in general type, but had derived its character from many primitive sources. As history dawns on the achievements of these early nations, it is interesting to note that there was a varied rainfall within this territory. Some parts were well watered, others having long seasonal periods of drought followed by periodical rains. It would appear, too, the uncertainty of rainfall seemed to increase rather than diminish, for in the valley of the Euphrates, as well as in the valley of the Nile, the inhabitants were forced to resort to artificial irrigation for the cultivation of their crops. It is not known at what time the Chaldeans began to build their artificial systems of irrigation, but it must have been brought about by the gain of the population on the food supply, or perhaps an increased uncertainty of rainfall. At any rate, the irrigation works became a systematic part of their industry, and were of great size and variety. It took a great deal of engineering skill to construct immense ditches necessary to control the violent floods of the Euphrates and the Tigris. So far as evidence goes, the irrigation was carried on by the gravity system, by which canals were built from intakes from the river and extended throughout the cultivated district. In Egypt for a long time the periodical overflow of the Nile brought in the silt for fertilizer and water for moisture. When the flood subsided, seed was planted and the crop raised and harvested. As the population spread, the use of water for irrigation became more general, and attempts were made to distribute its use not only over a wider range of territory but more regularly throughout the seasons, thus making it possible to harvest more than one crop a year, or to develop diversified agriculture. The Egyptians used nearly all the modern methods of procuring, storing, and distributing water. Hence, in these centres of warm climate, fertile land, and plenty of moisture, the earth was made to yield an immense harvest, which made it possible to support a large population. {154} The food supply having been established, the inhabitants could devote themselves to other things, and slowly developed the arts and industries.