“…The study of the origin of the rocks used to build the megalithic monuments in Brittany is relatively new. The stone material from the Barnenez cairn, Plouezoc'h, (Northwestern Brittany, Giot et al, 1995) and the great stelae of the Gulf of Morbihan (Southern Brittany, Bonniol & Cassen, 2009; Cassen et al, 2016; Querré et al, 2006) was analysed, revealing a displacement of over several kilometres. Analysing the three‐dimensional (3D) shape of megalithic slabs (Mens, 2008; Sellier, 1995, 2013) shows how the natural outcrops were exploited.…”