A fine example of 19th-century civil engineering, this railway and road bridge spans the River Ain, linking the towns of Bolozon and Corveissiat. Rebuilt after the Second World War (1950), it is 273 m long and comprises eleven arches on two levels.In 1865, the Conseil Général de l'Ain wanted to create a railroad line between Bourg-en-Bresse and La Cluse. To cross the Ain, the commune of Cize was chosen. Work began in 1870, and required extensive work on the foundations, including excavations at the bottom of the river. The materials used came from the immediate surroundings: gravel and sand from the river, stone from the nearby quarries of Bolozon, Grand-Corent and Corveissiat, and lime from Virieu-le-Grand and Le Teil.
Construction was completed in 1875, reaching a total length of 269 m and a height of 52 m. The two-storey structure comprises seventeen semicircular arches: eleven upper ones for rail traffic and six lower ones for road traffic.
The Simandre-Cize section opened on July 6, 1876, following completion of the Racouze tunnel and the opening of the Cize-Blozon station. The bridge was opened to road traffic in 1905. The single-track Carpathian line was operated until 1884 by the Compagnie des Dombes et des chemins de fer du sud-ouest, then by the PLM until 1938, when the newly-created SNCF took over. Today, the "Bourg-Genève" TGV high-speed train crosses the river via the viaduct.
On July 12, 1944, French resistance fighters launched an action on the viaduct designed to cut off rail communications and thus slow the advance of the Germans. They placed explosive charges under one arch of the road and another of the railroad. The explosions were only intended to slightly damage the viaduct, but proved fatal, destroying it almost entirely. As the viaduct has no supports at its ends, its deck is supported solely by the pillars. In barely twenty minutes, the pillars of the mined arches collapsed, destabilizing the structure and causing it to collapse completely. The impressive quantity of rubble even altered the course of the river!
The new viaduct was rebuilt almost identically between 1947 and 1950. A few modifications were made, however: the stone was largely replaced by concrete, the latter being reserved for cladding. The dimensions were slightly altered, particularly on the lower level, in response to requests from some mayors to widen the arched openings in the roadway.
