In the park behind the Castello Sforzesco, the spirit of Antiquity inspired Luigi Canonica's Arena and Luigi Cagnola's Arco della Pace, a triumphal arch built on the orders of Napoleon. Built in the 1930s by Gio Ponti and Cesare Chiodi, the Torre Branca is a fine metal structure rising to 104m and offering fine views of the city. The Acquario Civico, an interesting little aquarium, is now housed in a Liberty-style pavilion dating from the World Exhibition of 1906.