A geological curiosity, the clue de Sisteron is the patient work of the Durance. It has always been one of the rare crossing points between the Alps and Provence.
In Provence, the term “clue” refers to a narrow passage dug by a torrent perpendicular to a mountain range. Sisteron’s clue lies between two limestone formations of the same type, which were once continuous: the Baume rock and the Citadelle rock. These rocks were formed from a single large deposit of sediment at the bottom of the sea (during the Secondary Era), lifted and folded during the uplift of the Alps. Today, the hardest strata have resisted the erosion of the Durance River, leaving a narrow passageway that has been used by all communication routes since Antiquity. An essential link between the Alps and Provence, Sisteron was probably the site of the first stone bridge over the Durance in the 13th century.
The clue de Sisteron is also a climatic gateway – the limit of the olive grove – and a historic gateway between Provence and Dauphiné.
