jats:titleAbstract</jats:title>jats:pLevallois technology characterizes the Middle Stone Age/Middle Palaeolithic, but one of its earliest manifestations is from the preceding Acheulean of the Kapthurin Formation, in the Rift Valley of east Africa. Here, ~ 400 ka, hominins were creating large flake blank handaxes and cleavers through Levallois knapping. Comparing these tools with other Rift Valley Acheulean assemblages made on large flakes shows those of the Kapthurin Formation are distinguished by their thinness. This was achieved through symmetrical centripetal preparation of gentle upper surface convexities on the Levallois cores, the creation of a protruding facetted platform, and proximal bevelling of the upper surface. A large elongate flake blank was struck from the facetted platform, then finished with marginal trimming to create the symmetrical and regular edge of the handaxe or cleaver. As they were used for the creation of handaxes and cleavers, the Kapthurin Acheulean Levallois cores and flakes are much larger than that of the Middle Stone Age, with overshot flakes from excessive force a more frequent error. The Acheulean Levallois is further distinguished from those of the Middle Stone Age by the lack of recurrent flaking, with cores apparently producing only a single preferential flake without any repreparation of the main flaking surface, despite the cores being big enough for further large blank removals, and even if the preferential removal overshot and was abandoned. The key advantage offered by Levallois in general is large thin elongate flakes. In its Kapthurin Acheulean manifestation, Levallois was used to create an individual tool, but in the Middle Stone Age it was often used to make toolkits.</jats:p>