The documentary describes Siena through its Duomo, a treasure chest built by influential personalities and masters of art over eight centuries. Keeper of masterpieces that celebrate the events of Siena, the cathedral is a symbolic monument from which to look at history. The Battle of Montaperti, the Council of Nine, the heyday and fall of the Republic and the stay in of numerous illustrious artists in the city, such as Nicola and Giovanni Pisano, Duccio di Buoninsegna, Donatello, and Pinturicchio are just some of the events witnessed by the historical and artistic heritage of the Duomo, the film's absolute protagonist.