This large, vertical stone face with its Roman incription dating to the first half of the 5th century is also considered Le mystère de la pierre écrite (or the Mystery of the Written Stone).
The Pierre-Ecrite is located in narrowest part of the gorge of the "défilé de Pierre-Ecrite", a narrow valley along the Jabron river northeast of Sisteron.
The stone itself is not a mystery. It is well authenticated as being a 5th century text by Claudius Postumus Dardanus, with the help of his brother Claudius Lepidus. Claudius Dardanus was an influential man. A friend of Emperor Honorius, and is known partly for his correspondence with Saint Jerome.
The inscription speaks of making a passage to Théopolis (or the City of God), and fortifying the city against Barbarians. The mystery is that the location of Théopolis has never been positively identified. A possible location could be the ancient Roman site of the rock of Dromon southeast of the current Saint Geniez, but there is apparently no real evidence.
The inscription is fairly large, containing about 450 characters, with few abbreviations.
"Claudius Postumus Dardanus, patricien, ex-consulaire de la province viennoise, ex-prêteur des Gaules, et Nevia Galla son épouse, ayant fait couper les pans de la montagne de chaque côté, ont procuré un chemin viable au lieu dont le nom est Théopolis, lieu qu'ils ont fortifié par des murs et des portes ; le travail, fait dans leur propriété particulière et destiné à servir à la sécurité de tous, a été exécuté avec l'aide de Claudius Lepidus, compagnon et frère du sus-nommé."
Translated from the Latin inscription by Jean-Paul Clébot, Provence Antique, Robert Laffont Editor, 1992. Further translation into English by our amateur hand would not be beneficial.
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A 90-minute hike from the stone, up and along the ridge to Saint Geniez, is called the Route de Temps, possibly alluding to Saint Jerome, who was known for his very early thoughts about the concept of time.