The Cerdagne (Cerdanya in Spanish) is a part of the Pyrenees which after the Treaty of the Pyrenees of 1659 was divided between France which took the northern part and Spain which took the southern portion.
The Train Jaune (Yellow Train) follows a 62.6 km metre gauge route built in 1903-10 between Villefranche-de-Conflent and Mount-Louis and extended in 1927 to Latour-de-Carol, the frontier station between the French railway system (SNCF) and that of Spain (RENFE). There are 19 tunnels on the line, the longest of them 380 m and 337 m, and some notable bridges including the Séjourné Viaduct, which is 65 m high, and the 80 m high Pont Gisclara bridge. There are 22 stations along the line including one at Mont Louis whose fortifications by the French military engineer Sébastien Le Prestre de Vauban (1633-1707) have been designated a UNESCO World Heritage Site.
The route of the Train Jaune has from the time of its opening been electrified on the third rail system at 850 volts DC. Current is supplied from a specially-built hydro-electric power station at La Cassagne. Seven of ten original multiple units are still in use, some of them offering the option of open carriages, and there are units of 2004 which offer panoramic views and air conditioning. A journey along the whole length of the line takes two hours and twenty minutes. The line is operated by the French state railways (SNCF).