Until the Middle Ages, the need in stone for the construction of buildings could be satisfied by open-cast quarries. With the rise in demand, the methods evolved, and cavings were dug in order to extend the exploitation of the quarries without reducing and interfering with agriculture and demographic expansion.
All the monumental buildings (cathedrals, houses of dimension stones, the Louvre, the Haussmann buildings…) required an important quantity of stone and other mortars. All the material found on the surface left ever so many empty holes or more (with cutting waste) underground. So we discover true underground cathedrals when the mound of the filling material is not too high or a town under the town when the former quarries were filled in and consolidated (as is the case notably for the quarries of Paris which are wrongly called Catacombs).
These places which are very often dangerous, access being forbidden, are a historical heritage that is unfortunately too often forgotten. Who remembers nowadays that the hills of Chaumont or of Montmartre were practically twice as high before the mines below were artificially made to cave in? In these neighbourhoods where civilisation resettled in an unstable ground, you will often find a driller preparing for a concrete filling of the remaining voids which vary contingent on water infiltrations. Outside of Paris, the folly of real estate agents is fortunately held back by the presence of quarry voids. In the Paris area it can be considered that the remaining forests are often literally undermined.
These quarries or mines often fulfilled more than one role in their history (which sometimes dates very far back). Initially destined to yield material for various uses, they might later have served as cellar for a brewery, hide-away for bandits, passage for smugglers, in a not so long-ago period as civilian or military shelter during the world wars, underground factory for the bombs v1 or v2, bunker, to grow mushrooms, as a storage to sprout vegetable seedlings, or simply as storage for individuals or artists.
Let me guide you in this unrecognised, dark and silent world.
