Mont Cenis Tunnel

The Fréjus Rail Tunnel (also called Mont Cenis Tunnel) is a rail tunnel of 13.7 km (8.5 mi) length in the European Alps, carrying the Turin–Modane railway through Mount Cenis to an end-on connection with the Culoz–Modane railway and linking Bardonecchia in Italy to Modane in France. Its mean altitude is 1,123 m and it passes beneath the Pointe du Fréjus (2,932 m) and the Col de Fréjus (2,542 m).

The initial gallery was 12.8 kilometres long, twice as much as the previously longest tunnel. Drilling started in August 1857 from Bardonecchia and in December 1857 from Modane. At construction start, both ends were in Piedmont-Sardinia, but this changed with the transfer of Savoy to France in 1860 (Treaty of Turin). On 26 December 1870, French and Italian workers shook hands as the two teams met halfway: the galleries were aligned to about 40 cm horizontally and 60 cm vertically. The tunnel opened for traffic on 17 September 1871, thus making it the oldest of the large tunnels through the Alps. The gallery was extended to its present length in 1881 with a new reinforced entrance in more stable ground on the French side.

The construction, directed by Germain Sommeiller, was scheduled to take 25 years, but was completed in only 14 years thanks to technical innovations such as pneumatic drilling machines and electrical ignition of explosive charges. In the final construction years, the use of recently invented dynamite further accelerated the tunnel's completion. The next two Alpine tunnels were built with similar techniques: the Gotthard Rail Tunnel opened in 1882 and the Simplon Tunnel in 1906.

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