The Fréjus Rail Tunnel (also called Mont Cenis Tunnel) is a rail tunnel of length in the

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

, carrying the Turin–Modane railway through Mont Cenis to an end-on connection with the Culoz–Modane railway and linking

Bardonecchia Bardonecchia (; ; , ) is an Italian town and ''comune'' located in the Metropolitan City of Turin, in the Piedmont region, in the western part of Susa Valley. It grew out of a small village with the works for the Fréjus Rail Tunnel, the first c ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

Modane Modane (; ) is a Communes of France, commune in the Savoie Departments of France, department in the Auvergne-Rhône-Alpes Regions of France, region in southeastern France. The commune is in the Maurienne Valley, and it also belongs to the Vanoise ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

. Its mean altitude is and it passes beneath the '' Pointe du Fréjus'' () and the '' Col du Fréjus'' (). Headed by the Savoyard civil engineer Germain Sommeiller, construction of the tunnel commenced during August 1857, at a time when both ends of the future tunnel were in the

Kingdom of Sardinia The Kingdom of Sardinia, also referred to as the Kingdom of Sardinia and Corsica among other names, was a State (polity), country in Southern Europe from the late 13th until the mid-19th century, and from 1297 to 1768 for the Corsican part of ...

. From the onset, the tunnel was an ambitious engineering challenge, its gallery being twice the length of any tunnel previously constructed. Some figures believed that it would take as many as 40 years to complete; the total construction time was 13 years, the work having been greatly accelerated by the introduction of new technologies such as pneumatic drilling machines and

dynamite Dynamite is an explosive made of nitroglycerin, sorbents (such as powdered shells or clay), and Stabilizer (chemistry), stabilizers. It was invented by the Swedish people, Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern German ...

. On 17 September 1871, the Fréjus Tunnel was opened to traffic for the first time, facilitating a new era of interaction between France and Italy. The Fréjus tunnel remains an important link in the connection between

Rome Rome (Italian language, Italian and , ) is the capital city and most populated (municipality) of Italy. It is also the administrative centre of the Lazio Regions of Italy, region and of the Metropolitan City of Rome. A special named with 2, ...

and

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

, via

Turin Turin ( , ; ; , then ) is a city and an important business and cultural centre in northern Italy. It is the capital city of Piedmont and of the Metropolitan City of Turin, and was the first Italian capital from 1861 to 1865. The city is main ...

and

Chambéry Chambéry (, , ; Franco-Provençal, Arpitan: ''Chambèri'') is the Prefectures in France, prefecture and List of communes in France with over 20,000 inhabitants, largest city of the Savoie Departments of France, department in the southeastern ...

. Following the development of car and truck transportation, the Fréjus Road Tunnel was built along the same path from 1974 to 1980. During the 2000s, the Fréjus Rail Tunnel underwent a series of works to modernise and improve it, including the increase of its bore to accommodate wider rail vehicles, such as container trucks on piggy-back wagons, as part of the Autoroute Ferroviaire Alpine. A future high-speed rail tunnel to improve transit capacity between France and Italy, called the Mont d'Ambin Base Tunnel, is being planned as part of the Turin–Lyon high-speed railway project.

History

Background

The mountains of the

had posed long difficulties to any movements between Italy and its neighbours. Even with the arrival of new technologies such as the railway, the task of successfully traversing these peaks was viewed by numerous figures as a fool's errand, unfeasible to the point of being impossible. However, there was a strong political desire amongst officials in both Italy and France to establish a railway between the two which, if completed, would launch a new era of transit and bring new commercial opportunities for both nations. In Italy, the Victor Emmanuel Railway, which included both the Culoz–Modane railway across

Savoy Savoy (; )  is a cultural-historical region in the Western Alps. Situated on the cultural boundary between Occitania and Piedmont, the area extends from Lake Geneva in the north to the Dauphiné in the south and west and to the Aosta Vall ...

and the Turin–Modane railway across

Piedmont Piedmont ( ; ; ) is one of the 20 regions of Italy, located in the northwest Italy, Northwest of the country. It borders the Liguria region to the south, the Lombardy and Emilia-Romagna regions to the east, and the Aosta Valley region to the ...

, was largely constructed in the 1850s by the

and named after its king,

Victor Emmanuel II Victor Emmanuel II (; full name: ''Vittorio Emanuele Maria Alberto Eugenio Ferdinando Tommaso di Savoia''; 14 March 1820 – 9 January 1878) was King of Sardinia (also informally known as Piedmont–Sardinia) from 23 March 1849 until 17 March ...

. Prior to 1860, Sardinia had included both Savoy and Piedmont. Even as it was being first envisioned, the Fréjus Tunnel, a necessary feature for traversing Mont Cenis, was viewed as being the primary engineering challenge of the Turin–Modane railway by far; the initial length of its gallery was , which was twice as much as the previously longest tunnel in the world at that time. The Savoyard civil engineer Germain Sommeiller was appointed to head this undertaking. Considerable backing for the endeavor was forthcoming from individual Italians, not only in terms of funding, but also technical expertise, public endorsements, and labourers.

Construction

During August 1857, drilling work commenced on the

side; activity started on the Modane side in December 1857. It had been deemed impossible to increase the rate of excavation via intermediate shafts, thus the tunnel was driven entirely from either end. Serious challenges were encountered, including difficulty with providing sufficient ventilation. New methods of ventilation were successfully introduced, alongside other technological innovations. At the time, it was believed that, if the tunnel's construction had to rely upon traditional methods alone, it would have taken 71 years to complete. Three years following the start of the tunnel's construction, unanticipated political interactions led to the transfer of Savoy from Sardinia to

in 1860 under the Treaty of Turin; the change of borders did not majorly disrupt the rate of work on the tunnel however. The tunnel took 14 years to construct, its rate of progress having been considerably increased via the use of new technical innovations such as pneumatic drilling machines powered by compressed air. Ten drills were mounted in a frame to bore shot holes to receive blasting powder charges, with those in outermost positions aligned in a slight divergence from the centreline to increase the effective width. Air at a pressure of was conducted in iron pipes from

hydraulic compressor A hydraulic compressor is a means of compressing air using hydraulic energy. There are two very different types of machines referred to as hydraulic compressors. One type is a mechanical air compressor that is driven by a hydraulic motor. It is a ...

s, powered by local streams at the mouths of the workings. There were separate pipes for water jets to remove waste from the holes. Each firing required up to eighty holes, taking between six and eight hours to drill. On 26 December 1870, French and Italian workers shook hands as the two teams met halfway: the galleries were aligned to about horizontally and vertically. On 17 September 1871, the Fréjus Tunnel was officially opened to traffic. One foreign newspaper covering the occasion, the '' Michigan Argus'', described the tunnel as being "one of the greatest, if not the greatest, engineering feat of the age". While further major tunnels through the Alps have since been constructed, it has remained active, the Fréjus Rail Tunnel being the oldest of the large tunnels through the Alps. Between 1868 and 1871, the Mont Cenis Pass Railway was briefly operational as a temporary link over the Mont Cenis Pass. It was closed shortly after the opening of the Fréjus Railway. This railway was itself described as an engineering achievement in its own right.

Alterations and improvements

The original tunnel portal on the French side at Modane was only used for little over a decade before falling into disuse after having been bypassed during 1881. It was decided to redirect the tunnel to a new entrance positioned to the east of the original, where the ground was considerably more stable. The surplus portal was left in place as a monument, and has since become a minor tourist attraction. A steam locomotive has been placed in the disused portal, which is presently located adjacent to a road. During the 2000s, the Fréjus Rail Tunnel underwent a programme of works to both modernise and improve it. One specific and major alteration performed during this period was the enlargement of the bore to facilitate an equivalent loading gauge of French Lignes à grande vitesses (LGVs) throughout, thus enabling the tunnel to be traversed by wider rail vehicles, including container trucks on piggy-back wagons, as part of the Autoroute Ferroviaire Alpine. Various other enhancements were enacted, largely on the French side of the tunnel. The first package of work focused on civil works, while a follow-up package focused on electrical systems. During the former, the track was replaced and the track bed lowered, sections of masonry were repaired where applicable, new safety recesses created, along with other civil works around the tunnel's exterior, including a

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

Closure

On 27 August 2023, a major landslide occurred on the line close to the tunnel at Saint-André à La Praz. All traffic through the tunnel, including the major

TGV The TGV (; , , 'high-speed train') is France's intercity high-speed rail service. With commercial operating speeds of up to on the newer lines, the TGV was conceived at the same period as other technological projects such as the Ariane 1 rocke ...

and Frecciarossa services between the

Gare de Lyon The Gare de Lyon, officially Paris Gare de Lyon (), is one of the seven large mainline railway stations in Paris, France. It handles about 148.1 million passengers annually according to the estimates of the SNCF in 2018, with SNCF railways and ...

and Milan Centrale / Porta Garibaldi were suspended. Repairs were complicated and the line remained closed until spring 2025.

Neighbouring fortifications

Following the transfer of

from Italy to France, the Fréjus Tunnel became a possible invasion route from Italy to France, particularly as it avoided the historical difficulties posed by the Mont Cenis pass. Accordingly, an extraordinary amount of defensive fortifications were constructed near to and around Modane. The Fort du Replaton and the Fort du Sapey were built in the late nineteenth century on the heights across the valley of the Arc. During the 1930s, the

Alpine Line The Alpine Line () or Little Maginot Line (French: ''Petite Ligne Maginot'') was the component of the Maginot Line that defended the southeastern portion of France. In contrast to the main line in the northeastern portion of France, the Alpine Line ...

fortifications

Ouvrage Saint-Gobain Ouvrage Saint-Gobain is a work (''gros ouvrage'') of the Maginot Line's Alpine extension, the Alpine Line. The ouvrage consists of one entry block, one infantry block, one artillery block, one observation block and one combination block. Located ...

Ouvrage Saint-Antoine Ouvrage Saint-Antoine is a work (''gros ouvrage'') of the Maginot Line's Alpine extension, the Alpine Line. The ouvrage consists of one entry block, one infantry block and one artillery block overlooking Modane on the way to the Col du Mont Ceni ...

and additional fortifications at Le Sappey were also constructed. A blockhouse along the rail line to the east of the modern tunnel entrance has become a tourist attraction. The ''maison penchée'' ("leaning house") was built in 1939 to guard the tunnel entrance over an ammunition magazine connected to the tunnel by a gallery. During 1944, the retreating Germans deliberately exploded two rail wagons inside the tunnel entrance, causing the magazine to explode and blasting the blockhouse off its foundations, leaving it on a tilt.

References

{{DEFAULTSORT:Frejus Rail Tunnel Tunnels in the Alps Railway tunnels in Italy Railway tunnels in France Transport in Piedmont France–Italy border crossings Savoie Tunnels completed in 1871 1871 establishments in Italy 1871 establishments in France Bardonecchia