The history of French cartography can be traced to developments in the Middle Ages. This period was marked by improvements in measuring instruments and also by an upgrade of work in registers of all types. What is thought to be the oldest land map in Europe, the Saint-Bélec slab, representing an area of the Odet valley, was found in 1900, and rediscovered in a castle cellar in France in 2014. The Bronze-Age stone is thought to be 4,000-years old.