During the early post-Pleistocene there flourished right across the middle belt of the African continent a highly distinctive way of life intimately associated with the great rivers, lakes and marshes. This belt–or arc, to be more precise, corresponding roughly with the drought zone of the early 1970s–comprises the southern Sahara and the Sahel from the Atlantic to the Nile and there bends up-river to the East African rift valleys and the equator. Traceable as early as the eighth millennium BC, the zenith of this ‘aquatic civilization’ was achieved in the seventh millennium, being a time when higher rainfall made rivers longer and more permanent and caused lakes to swell and burst their basins (Butzer et al., 1972; Zinderen Bakker, 1972). Around 7000 BC, for instance, fish populations as well as hippos and crocodiles reached the central Saharan highlands, while, to their south, Lake Chad expanded enormously till it overflowed via the Benue and Lower Niger into the Atlantic. In East Africa at the same time the small lakes in the Kenya rift valley rose to combine or to create riverain links over the normal watersheds, while to their north Lake Rudolf reached a height sufficient to help feed the White Nile system.
