=1. The Land.=--The Mesopotamian Valley, as the great region watered by the Tigris and the Euphrates Rivers is called, in many respects resembles Egypt, although in other respects it differs strikingly from Egypt. The country is like Egypt in that it is formed by rivers; it differs from Egypt in that it has two rivers instead of one. In late geologic time the Persian Gulf extended far up toward the Mediterranean. All of what was Babylonia has been formed by detritus (silt) brought down by the Tigris and the Euphrates. The process of forming land is still going on. At the head of the Persian Gulf about seventy feet a year is still formed in this way, or a mile in about seventy-five years. Both the Tigris and the Euphrates rise in the mountainous regions of Armenia, on opposite sides of the same range of mountains. The melting of the snows on these mountains gives both rivers, like the Nile, a period of overflow. As the source of the Tigris is on the south side of the mountains, it begins to rise first. Its rise begins about the first of March, its overflow is at its height in May, and the water recedes in June or July. The Euphrates begins to rise about the middle of March, continues to rise until June, and does not recede to its ordinary level until September. The soil thus formed is of rich materials, and the retreating flood leaves it each year well watered and softened for agriculture. Here, as in Egypt, one of the earliest civilizations of the world developed. It was quite independent of that in Egypt, and consequently differed from the Egyptian in many respects. Unlike Egypt, Babylonia had a rainy season; nevertheless she was mainly dependent upon the overflow of the rivers for her irrigation and her fertility. As she possessed two rivers, her breadth was greater than that of Egypt, but she lacked the contiguity of protecting deserts, such as Egypt possessed. All through her history her fertile plains attracted the mountain dwellers of the East and the peoples of the West. Subject to frequent invasion by these, Babylonia had no long peaceful development such as Egypt enjoyed before the Hyksos invasion. From before the beginning of written history race mingled with race in this great valley, invasions were frequent, and the construction of permanent empires difficult. [Illustration: MAP OF BIBLE LANDS]