LONG before Egypt was united into a single kingdom, the southern portion of the plain, watered by the lower courses of the Euphrates and the Tigris, was the home of a settled people. Here, if the sun was more scorching than in Egypt, the soil could be made even more productive. The land near the ancient mouths of the rivers consisted of rich alluvial earth, which, under irrigation, yielded plentiful crops ; this was the site of the Biblical Garden of Eden. Of this land, the northern and less fruitful portion was called Akkad and the southern Sumer. The district of Sumer must have been in settled occupation long before 5000 B.C. Excavations at Ur of the Chaldees in southern Mesopotamia (" the land between the rivers ") have uncovered a bank of clay eight feet deep, which could have been deposited only by a flood of very long duration. Underneath the clay were further remains of human habitation. Thus the Old Testament story of the Flood is based on more than an empty myth. The Sumerians belonged originally to the Indo-European peoples, who from the earliest times had roamed on the grasslands which extend from the Danube far into Asia. These peoples, originally of one stock, called Aryan, divided early into various tribes, which developed different languages, and, with their horses and wheeled carts, roamed over the steppes, living a semi-agricultural life. One section invaded northern India in the second millennium B.C. and established its rule in Hindustan. The western section has, at different epochs, when a drought has dried the pastures, let hordes of invaders loose upon the more fertile land to the south. In Italy and France, in Greece and Asia Minor, nomadic conquerors have thus, at various times, driven out or enslaved the aboriginal populations. But it is in Mesopotamia that an Indo-European people first encountered the Semites.