SIMPLON, a pass of the Alps, between Switzerland and Italy, in the east of the canton of Valais, celebrated for the road which was constructed over it by order of Napoleon I. This is one of the greatest works of engineering in modern times. It is 38 miles long, from Brieg in Valais to Domo d'Ossola in Piedmont; its height is 6592 feet above the sea; its breadth from 25 to 30 feet; and in its course it is carried over 611 bridges, and through many tunnels.