Towards the end of the Tertiary a period of extreme aridity must have brought river action to a stillstand, whilst the upwarping of the continent created a big potential of erosion for the Early Pleistocene pluvials. These pluvials are therefore represented by an incision of all the major rivers. The first Pleistocene gravels, present in all the river systems, belong to the Kanjeran pluvial. The terraces of this stage are always calcified and have yielded abundant Late Chelles-Acheul tools. Fauresmith assemblages are rare. It is not yet certain whether this is due to climatic circumstances or to the comparatively short duration of this transition culture, or both. The Late Pleistocene pluvial is well represented by non-calcified gravel terraces containing South African Middle Stone Age implements. Later M.S.A. assemblages are rare and confined to the neighbourhood of springs showing thus the approach of a new arid phase, during which the Kalahari dunes were on the move again. The latest phase of the M.S.A. seems to be completely lacking. When climatic conditions became more favourable again the country was occupied by people practising a Smithfield culture. Typical Wilton seems to be confined to the Kalahari fringe. Keywords: Namibia, Namib desert, Kalahari Desert, Kuiseb River, Swakop River, Fish River, palaeoenvironment, palaeoclimate, prehistory, desert archaeology, stone artifacts, river systems, climatic events, climate change, aridity, aridification.