What is Florence known as in the novel, The Agony and the Ecstasy?

Florence is known as the city of stonecutters, whose very streets are paved with such craftsmanship they outdo the architecture of other places. The city is replete with pietra serena, the serene, easily-workable stone from the surrounding mountains. The duomo, perhaps the most visible symbol of the start of the Renaissance, overlooks the city.