La Scala was inaugurated in 1778, just two years after the United States declared freedom from Britain, and to this day, the season opening of the Milanese opera house is a society event. This exhibition probes 240 years of the theater’s architectural history: how it has changed with the times, how it has maintained its centuries-old stature, and how its restoration by the Swiss architect Mario Botta, due for completion in 2022, meets the moment. —J.V.