The town of Sisteron extends near the confluence of the Buëch and the Durance at the place where the Durance crosses the Baume cluse. On a site easy to fortify, the city and its fortress monitoring the only bridge over the Durance have been the subject of much covetousness over the centuries. The ancient Segustero became a strategic crossing point from the construction of this bridge (now called Baume bridge) in the Gallic era. Its essential role in the region earned Sisteron a millennial influence that led to very early fortification and special administrative status. Sisteron lost its importance with the multiplication of the crossings over the Durance in the 19th century.