The central mountain mass (9850 ft. high) of the Middle Alps and core of the whole Alpine system; it forms a watershed for rivers flowing in four different directions, including the Rhône and the Rhine; the famous pass (6936 ft.) from Lake Lucerne to Lake Maggiore forms an excellent carriage-way, has two hotels and a hospice at its summit; on the lower slopes is the St. Gothard railway (opened 1882), with its celebrated tunnel (9¼ m.), the longest in the world.