Abstract In July 2007 an important archaeological find was made in the Op de Schans loess pit near Kesselt (Belgian Limburg) immediately to the west of the Dutch city of Maastricht. During an archaeological rescue dig, three Lower Palaeolithic artefacts were recovered from the infill of an ancient erosion gully: a bifacial side-scraper, an atypical biface and a cortical flake. Typologically, the artefacts can be classified as Acheulean. In this region, harbouring several such brickyard pits, these are the oldest artefacts yet found, prompting further investigations into the stratigraphic position of the archaeological layer. The Op de Schans pit, which has yielded several Middle Palaeolithic occupation horizons, is located in the middle of an ancient sediment trap. Because of this exceptional geomorphologic situation, multiple ancient sediments have been preserved which elsewhere were entirely removed during subsequent erosion phases. Here five separate loess beds with intercalated interglacial palaeosols are present, overlying the deposits of the River Maas (Meuse). This sequence has been used as a hypothetical framework for elaborating a chronostratigraphic model. The archaeological level in question, discovered at the base of a subsequently infilled erosion gully, can most likely be chronostratigraphically dated to around the start of Marine Isotope Stage 10 (MIS 10), in the era of the Pottenberg discordance (approx. 390 ka). However, the possibility cannot be excluded that the gully in which the artefacts were found dates from an early phase of MIS 12 (approx. 480 ka). The age may in fact be greater still, as the artefacts have been eroded out of their original, primary context and subsequently deposited in the gully. Hypothetically, they may even have been taken up from the Maas loam of the Kesselt Maas terrace (MIS 13) that here is situated directly below the archaeological horizon. This would make the maximum age of the artefacts recovered from the gully around 500 ka.