In the valley, the annual flood of the Nile continuously changed the lay of the land. When the water overflowed the river banks the silt, previously kept in suspension by the speed of the swollen current, precipitated. Some of this precipitation raised the river bed, the remainder covered the banks and the area closest to them; towards the edges of the valley there was comparatively little deposit. Thus banks of considerable height were formed, and after some years the weight of water broke through these natural dikes to seek a new course in low-lying parts, some distance away. The old bed turned into swamp, but its banks remained as ridges and hillocks whose height and area were increased by wind-blown dust and silt caught at their edges. Trees took root, and man settled there, sowing his crops and grazing his beasts in the adjoining lowlands, to retire with them to the high ground of the old banks when the river overflowed. During the inundation, fish, wild boar, hippopotamus, and huge flocks of water birds invaded the surrounding fields and supplied an abundance of food throughout the summer. All traces of these settlements in the valley proper have long since disappeared; they have been not merely silted over but washed away by the changes in the river’s course.[65] This explains why we find traces of early settlements only at the edge of the valley, on the spurs of detritus at the foot of the high cliffs. We must imagine the valley, not flat and featureless as it is to-day, but dotted with hamlets perched on the high banks of former watercourses and surrounded by an ever-changing maze of channels, marsh, and meadow. Even as late as the First Intermediate period, just before 2000 B.C., the populace of a province in Middle Egypt left their homes and hid in swamps in the valley to escape the dangers of civil war and marauding soldiers.[66] And the early predynastic settlements at the valley’s edge were built in groves; among the remains of huts and shelters, tree roots of considerable size have been found.[67]