Susa (503m/1,660ft; pop. 7,000) is an old town, beautifully situated between high mountains, which controlled the Montgenèvre and Mont Cenis roads. On the west side of the picturesque old town, on the right bank of the Dora, rises a marble triumphal arch (13.5m/44.5ft high) erected in 8 B.C. in honor of the Emperor Augustus by the prefect Cottius
, after whom the Cottian Alps are named. Northeast of the arch stands the cathedral of San Giusto (11th-13th centuries), with a beautiful campanile. At Susa the road forks: Montgenèvre to the left, Mont Cenis straight ahead. The road to Mont Cenis (S.S. 25), constructed by Napoleon in 1803-10, runs uphill, with numerous curves and sharp bends.