Ludovico I (1416–75) started the Golden Age of the city and imposed himself as a mediator between the neighbouring powers. Ludovico II constructed a tunnel, no longer in use, through the Monviso, a remarkable work for the time. With the help of the French he resisted a vigorous siege by the Duke of Savoy in 1486, but in 1487 yielded and retired to France where he wrote L'art de la chevalerie sous Vegèce ("The art of chivalry under Vegetius", 1488), a treatise on good government, and other works on military affairs.