In the Middle Ages, pilgrims passing through
Moncenisio and
Susa Valley came to
Turin along a road called the
Via Francigena, with a final destination of Rome. In 1414,
Niccolò III d'Este, Marquis of Ferrara, travelled on this route returning from Paris having met
Charles VI, and described the Col du Mont Cenis as having "a good ascent and bad descent". This pass was crossed in 1689 by the Vaudois, and is believed by some authors to have been
the pass used by Hannibal to cross the Alps. As an Alpine pass, Mont Cenis featured in several historical incidents. One example is the descent of
Constantine I to Italy, to fight against
Maxentius. It was the site of a military victory by the French
Army of the Alps, led by General-in-Chief
Alex Dumas over
Piedmontese forces in April 1794, a victory that enabled the French
Army of Italy to invade and conquer the Italian peninsula. It was the principal route for crossing the Alps between France and Italy until the 19th century. It was also used as the main passage by which
Charlemagne crossed with his army to invade
Lombardy in 773, and later by Napoleon I. Mont Cenis was one of the most-used Alpine passes from the Middle Ages to the nineteenth century. The pass was part of the border between the two countries from the
annexation of Savoy to the Second French Empire in 1861 until the 1947
Treaty of Paris, but is now located completely in France. The treaty allowed
Savoy to retrieve its historical and political boundaries. It has historically been part of
Route nationale 6. A road over the pass was built between 1802 and 1805 by
Napoleon to improve military connections. By 1810, it was the most-travelled road between France and Italy, as
Strasbourg was closed to
silk trade traffic from
Vienna, leading to
Lyon becoming a major trade centre instead. The
Mont Cenis Pass Railway was opened alongside the road in 1868, but was dismantled in 1871, on the opening of the
Fréjus Rail Tunnel. It was the first-ever railway based on the
Fell mountain railway system and was worked by English engine-drivers. The Fréjus Rail Tunnel acquired the alternative, and geographically incorrect, name of Mont Cenis Tunnel because the traffic which formerly used the Mont Cenis Pass was transferred to it. When the
Kingdom of Sardinia-Piedmont ceded Savoy to France in 1860, the Mont Cenis became a frontier pass, and consequently, a part of Savoy was left on the Italian side. It was, therefore, highly fortified as a protection against an invasion of the Val di Susa route towards Turin. In 1874–1880, the Italian
Regio Esercito built three stone forts: Fort Cassa, Fort Varisello, and Fort Roncia, supported by several batteries and fortifications, such as those at the top of
Mont Malamot. Two further armored batteries, La Court and Paradiso, were added in the early 20th century, while the
Fascist government built here part of its underground
Alpine Wall. All these fortifications are now in French territory after the boundaries revision in 1947, allowing Savoy to get its historical territory back. The
Lac Du Mont Cenis is an artificial dam that was constructed in 1921 on top of the original road and border crossing. It feeds two hydroelectric power plants. The lake is occasionally drained for maintenance. ==Cycling==