The Saint-Belec slab. (D. Gliksman/Inrap) A piece of rock with mysterious markings that lay largely unstudied for 4,000 years is now being hailed as a "treasure map" for archaeologists, who are using it to hunt for ancient sites around north-western France. The so-called Saint-Belec slab was claimed as Europe's oldest map by researchers in 2021 and they have been working ever since to understand its etchings – both to help them date the slab, and to rediscover lost monuments. "Using the map to try to find archaeological sites is a great approach. We never work like that," said Yvan Pailler,...