Simplon, pass, 6,590 ft (2,009 m) high, in the Lepontine Alps, Valais canton, S Switzerland. It is crossed by the Simplon Road built (1800-1806) by Napoleon I. The Simplon Railway passes through Simplon Tunnel I and II, one of the longest (both 12.3 mi/19.8 km) in Europe. Opened in 1906 and 1922, respectively, the tunnels cross the Swiss-Italian border from Brig to Isella. They have a maximum elevation of 2,313 ft (705 m). The Simplon Pass has been an important trade route between northern and southern Europe since the 13th cent.