During the works for the construction of the buildings of the Chamber of Commerce and the Stock Exchange, have emerged, starting from 1880, stretches of the impressive foundations, portions of the elevation and of the architectural decoration of the old theater, built at the end of the first century BC Mediolanum, which recently became a Roman municipium (49 BC at the time of Julius Caesar).
Theater performances, in addition to recreation and entertainment, were also functional to the spread of the Latin language and culture of the Celtic tradition as the center Mediolanum. The heavy mass of the theater (approx 20 m high with a diameter of 95 m and a capacity of about 8000 spectators) rested on massive foundations conglomerate of pebbles and mortar, over a land previously consolidated digging large wooden poles.
The memory of the location of the theater, gradually dismantled during the Middle Ages, has been maintained over time through the place names, especially in via San Vittore al Teatro.