At 500 m above sea level, the citadel of Sisteron overlooks the city of Sisteron - located in a passage between Dauphiné and Provence - and the Durance . Built on a rocky outcrop, is the first thing arriving in the city we see. The citadel, with its fortifications , was a strategic bolt on the road of the Alps to the Mediterranean . Classified historic monument is the centerpiece of the city. Jean Errard , military engineer of Henri IV , andVauban have left their mark.