The geology of a ghost city
The Chaos de Montpellier-le-Vieux is a 120-hectare geological park of ruin-like rock formations on the Causse Noir, a limestone plateau in southern France. The story of this "City of Stones" begins 170 million years ago, during the Jurassic period. A shallow, tropical sea covered the region, and the skeletons of marine organisms accumulated on the seafloor, eventually forming a thick layer of dolomitic limestone.
The landscape's transformation from a flat seabed to a chaotic labyrinth started around 100 million years ago with the tectonic uplift that formed the Alps and Pyrenees. This process raised the Grands Causses plateaus and fractured the dolomite bedrock, creating a network of cracks and fissures. For millennia, rainwater, made slightly acidic by absorbing atmospheric carbon dioxide, seeped into these fractures. This weak carbonic acid preferentially dissolved the rock, a process known as karstification. Water and freeze-thaw cycles widened the cracks, carving the stone into the strange pinnacles and towers seen today. This specific type of landscape is known as a blockfield or a "stone forest." The shapes are so evocative that many have been given names, such as the Gate of Mycenae, the Queen's Face, and the Elephant.
An ecosystem shaped by stone
For centuries, the rugged terrain kept the area largely uninhabited and shrouded in legends of curses and witchcraft. It was not until 1884 that the French speleologist Édouard-Alfred Martel systematically explored and mapped the site. Martel, considered a founder of modern speleology, demystified the landscape by explaining its geological origins and giving many of the rock formations the names they still bear today. His work transformed the perception of the "old heap of stones" from a cursed place into a natural wonder.
The complex topography creates a variety of microclimates that support a surprisingly diverse ecosystem. Arid, sun-exposed tops of the dolomite blocks differ from the shaded, humid conditions in the narrow passages between them. This allows for a mix of flora, including hardy Scots pines, pubescent oaks, and numerous species of rare orchids adapted to the limestone soil. The wider Grands Causses region, of which the Causse Noir is a part, hosts wildlife such as griffon vultures, golden eagles, roe deer, and beavers. The park's biodiversity comes from its unique geological structure.