Abstract From 1920 to 1990, these brave geologists travelled through the Sahara from Mauritania to Libya and from Algeria to Niger. During these hikes across thousands of kilometres, often in very difficult conditions, they were able to trace the main features of the geology of these desert regions, they established stratigraphical sections of the main sedimentary provinces, discovered volcanic and eruptive complexes and drew geological maps of large areas. Today, helicopters, four-wheel-drive vehicles, satellite observations and global positioning systems allow people to visit the most remote regions of the Sahara safely; however, geologists, naturalists and explorers like Chudeau, Kilian, De Lapparent, Monod made the most of their observations and discoveries thanks two essential auxiliaries: the camel and the goatskin bottle. The portraits and the principal contributions to the geology of the Sahara of these four pioneers are presented here with maps of their itineraries.