Rotonde ferroviaire de Montabon, Railway roundhouse in Montval-sur-Loir, France.

The Rotonde ferroviaire de Montabon is a semicircular railway roundhouse in a small French village along the Loire. It has 10 tracks inside served by a rotating turntable that connects to the national railway network.

Built between 1889 and 1891 for the Chemins de fer de l'État, the roundhouse served the Paris-Bordeaux line that opened through Château-du-Loir in 1886. After the 1938 SNCF merger, the ex-Paris-Orléans route was preferred and this line declined. The depot closed in 1954 and stood abandoned until 2009, when François Leboucq bought it to prevent demolition; it was listed as a monument historique in 2010.

The roundhouse is a type État building, a designation tied to the Chemins de fer de l'État, whose 1886 Paris-Bordeaux line made Château-du-Loir a stop. The association Rotonde ferroviaire de la vallée du Loir, which bought the site in 2017, keeps it and its preserved railway equipment. In 2018 the Mission patrimoine led by Stéphane Bern selected it among eighteen endangered national sites.

The roundhouse stands in Montabon, near the Château-du-Loir station in Montval-sur-Loir, on level ground reached from the village road. The building is a private historic monument cared for by the association Rotonde ferroviaire de la vallée du Loir; access to the interior depends on the association, so check its openings before travelling. The site is not a museum with regular guided tours.

Unlike many other preserved railway buildings in France, this one stays connected to the active railway network and is not just a museum. This means real trains can still be seen using the adjacent tracks today.