Cenis, Mont (môN sənēˈ) [key], Ital. Moncenisio, Alpine pass, 6,831 ft (2,082 m) high, on the French-Italian border. It is one of the great invasion routes in Italian history. Napoleon I built a new road there in 1810. In 1871, the Mont Cenis railroad tunnel (Frejus Tunnel) was built approximately 30 mi (48 km) away, connecting the towns of Mondane, France and Bardonecchia, Italy. As the first rock tunnel of its sort, it pioneered many techniques and represents a landmark in engineering. It is still one of the world's largest (8 mi/13 km) railroad tunnels.