A 2 km section of the Paris-Chartres railway line was never built, specifically the tunnel under Sceaux and Fontenay-aux-Roses between Châtenay-Malabry and Bagneux. The line was launched in 1907 with the goal of connecting the Paris-Chartres line via Gallardon to Paris, but it lacked the final 2 km of tunnel needed to reach the capital. The line only operated from 1930 to 1939, with only two daily round trips—considered impractical by historian Clive Lamming. Today, the Fauvettes viaduct, completed in 1913, remains as a notable remnant and hosts over 130 climbing routes. The Paris-Chartres line was declared of public utility in 1903, connecting Paris to Chartres and intended to complete the Paris-Bordeaux link built by the state. However, construction began from Chartres rather than Paris, as the name might suggest. In 1909, the state acquired the Compagnie de l'Ouest, which already owned the existing Paris-Chartres line, making the new line obsolete for long-distance travel. Despite this, construction continued slowly with plans for four tracks between Paris and Massy. Key sections of the line were completed in various years: the Chartres-Gallardon-Pont section in 1913, Saint-Arnoult in 1917, Limours in 1922, and Châtenay-Malabry in 1931. The Chartres bridge was built from 1919 to 1923, and the Gallardon bridge in 1928, allowing the Sceaux line and the Grande Ceinture to cross over the future tracks. The land for the last section was acquired before World War I, but the 2 km under Sceaux and Fontenay-aux-Roses was never built. This is confirmed by Wikipedia and the text of railway historian Clive Lamming. On the Paris side, a section existed between the West Ceinture and Montrouge-Châtillon, but it was never opened for commercial service and was used only as a service track between Montparnasse and the Montrouge-Châtillon depot. Thus, two sections of track faced each other, separated by a gap. The line diagrams still indicate the beginning of the never-built section at Bagneux. The land reserved for the last section remained unused until the creation of the Avenue du Général-de-Gaulle in 1980. The TGV line, built from 1987 to 1989, eventually provided railway use in Massy within a concrete casing that runs diagonally under the Chartres and Gallardon bridges. The Paris-Chartres line opened on May 15, 1930, only between Chartres and Massy-Palaiseau. At most, two round-trip trains per day ran on it, with schedules considered impractical and discouraging. No express train ever ran between Paris and Gallardon. The passenger service was interrupted as early as September 1939. The Massy-Gallardon section was damaged during World War II, and the rails were removed after the liberation. The section was finally decommissioned on November 28, 1953. An Allied bombing in 1944 damaged an arch of the Fauvettes viaduct, which was never repaired, and traffic never resumed. The Fauvettes viaduct, completed in 1913, crosses the Yvette valley over 221 meters with 12 arches and a height of 34 meters. Located on the communes of Gometz-le-Châtel and Bures-sur-Yvette, it reopened to the public in October 2004 after consolidation work started in late 2003. It offers more than 130 climbing routes from 7 to 36 meters high and is nicknamed "the highest cliff in Île-de-France." Its pillars range from 7 meters at the ends to 34 meters in the center. The GIGN and RAID also train there. To see the gap on the Paris side, it is enough to pass under the Chartres bridge, which allows the Sceaux line, now the RER B, to cross over rights of way that never hosted a single passenger train towards Paris.