This river-valley, the like of which in nature and formation is not to be found in the whole globe, offered in its seclusion a peculiarly favoured spot. It was a small green oasis of luxuriant fertility and grateful coolness in the midst of boundless deserts. The dwellers in a land whose soil was every year newly manured by nature, which brought forth abundantly almost without labour, must very soon have abandoned a pastoral life for agriculture, and in consequence have acquired fixed abodes and settled possessions. But the yearly inundation compelled them also at an early period to protect their flocks from the water, to secure their habitations, to observe the periods of the rising and falling of the stream. The long duration of the overflow made it necessary to provide for the support of man and beast. They had to learn how to carry on their dealings with each other upon the water, when the whole valley was still filled with the river, and to mark out firmly the limits of their plots, so that they might again take possession of them after the inundation. In Nubia the cataracts stopped the navigation of the river, and the lines of rock and strips of desert made intercourse difficult, and confined the life of the tribes within the limits of the native valley to their separate possessions. In Egypt, within the two lines of hills, land and river created no hindrance. A region so concentrated could not but carry the tribes beyond the limits of separate existence; the very land forced them to live a life more in common. There was only a slight natural distinction between the more secluded upper valley and the lower opening in the Delta about the mouths of the Nile; and this could merely have a stimulating effect upon the development of culture, without interfering in any way with its unity. Nevertheless the community of life in the valley of the Nile was not caused solely by the nature of the land. The tribes of the deserts around this long and narrow oasis must have had all the more lively a sense of the charm of the favoured valley owing to the difficulty with which they procured their own subsistence. Against these plundering neighbours, and their attempts to force themselves into the valley of blessing and abundance, the inhabitants of Egypt had to combine their forces. They needed a strong centralized command, a warlike monarchy, to which here, earlier than elsewhere, the patriarchal government of the tribes would therefore give way.