The primary sources of diamonds for the Namibian placers were the abundant and fertile kimberlite pipes situated on the KaapVaal craton in the southern African hinterland. Other contributions have been derived from sedimentary units that acted as intermediate hosts or secondary reservoirs for alluvial diamonds. These secondary hosts range in age from the Archaean (more than 2.7 billion years ago) through to the Cretaceous (about 70 million years ago). From some 100 million years ago, the long-lived Orange-Vaal drainage system has been the main fluvial conveyor moving vast quantities of eroded sediment from the interior of southern Africa to the Atlantic Ocean. Since Early Tertiary times (about 65 million years ago), continental uplift promoted the formation of a steep, bedrock-incised Orange River that provided ample natural attrition opportunities for the upgrading of diamond quality from source to sink. Sea level variations and continental tectonic movements influenced relative base level changes from the Orange River mouth upstream, promoting the formation of diamondiferous gravel terraces along the lowermost reach only. These river borne (fluvial) placers formed some 17 to 19 million years ago and again at some 3 to 5 million years ago. Significantly, the older terrace suite has proved to be more economically interesting than the younger gravel deposits.