By the end of the 1870s Eiffel & Cie, the company formed by Gustave Eiffel in partnership with Theophile Seyrig, had an established position among the leading French engineering companies. Between 1875 and 1877 the company had built the Maria Pia Bridge over the Douro at Porto, and when it was proposed to construct a railway between Marvejols and Neussargues in the Cantal department the work of constructing a viaduct to cross the River Truyère was given to Eiffel without the usual process of competitive tendering at the recommendation of the engineers of the state Highways Department since the technical problems involved were similar to those of the Maria Pia Bridge; indeed, it was Eiffel & Cie's success with this project that had led to the proposal for a viaduct at Garabit.
When it opened with a single track in November 1885, the Garabit Viaduct was 565 m (1,854 ft) long and weighed 3,587 tonnes (3,530 long tons; 3,954 short tons). Even more impressive was the actual deflection, which was measured at 8 millimetres (0.315 in), a figure precisely anticipated by Eiffel’s calculations. The bridge was also, when built, the highest in the world at 124 m (407 ft) above the river. The overall project cost was 3,100,000 francs. Until 11 September 2009, only one regular passenger train per day in each direction used to pass over the viaduct - a Corail route from Clermont-Ferrand to Béziers. On that date, the viaduct was closed as cracks were discovered in one of the foundation piles. It reopened one month later after a safety inspection and has been in service since then with a speed limit of 10 km/h (6 mph) for all traffic.
The Garabit Viaduct was used to represent the condemned "Cassandra Crossing" bridge in the 1976 film The Cassandra Crossing. In the film the Cassandra Crossing has been unused and derelict for 30 or 40 years and is considered dangerous, to the extent that people living nearby moved away fearing it could collapse.