Quantifying fluvial incision rates is key to understanding landscape evolution over Quaternary timescales, particularly in tectonically and climatically dynamic settings. 26Al/10Be burial dating of alluvial endokarstic deposits preserved in cave systems provides a powerful tool to constrain such rates. We apply this approach to the ~80 m-deep Save River gorges in the Pyrenees foreland (Haute-Garonne, France), where incision into Eocene limestones has generated a multi-level karst network. In this setting, however, clasts may have experienced (i) complex pre-burial exposure histories, including potential intermediate storage within the Lannemezan megafan, and/or (ii) post-depositional intra-karst reworking. To address these issues, we employ the isochron method, which enables robust identification and rejection of outliers and improves burial age estimates. Twenty-one quartz-bearing pebbles were collected from three cave levels spanning ~40 m in elevation, with the highest and lowest caves located ~55 m and ~20 m above the modern river, respectively. After exclusion of a single outlier, isochron burial dating yields three consistent Middle Pleistocene ages (~600–700 ka) despite the potential complexities noted above. These results suggest (i) peak incision rates exceeding 0.2 m/ka and (ii) that at least roughly half of the gorge depth formed during a single incision phase. They further imply a marked reduction in incision rates over the past ~600 ka (~0.03 m/ka). We tentatively relate this incision pulse to a regional base-level fall in the Garonne-Save system associated with the Mid-Pleistocene Transition, although a contribution from post-orogenic uplift cannot be excluded.