Guided tour of five remarkable railway viaducts 150 years old and still in service. They are located on the Commentry-Gannat line and cross the valleys of Bouble and Sioule . The viaducts of la Bouble, du Bélon, de Rouzat and de Neuvial are metallic, inscribed by the state services as historical monuments and remarkable natural sites. The Perrière viaduct is built of granite stone and its shape is curved. These five works have been recognized by "Aurhalpin Heritage" as a Remarkable Industrial Ensemble.