The Cathedral of Siena is a cathedral in Romanesque-Gothic style, one of the highest expressions of this style, typical for the white and dark green marble cladding, which recall the colors of the city. Its plan has the shape of a Latin cross with three naves. Inside, everything is a work of art, starting with the floor, defined by Vasari: "The largest, most beautiful and magnificent, that has ever been made". The inlays were all composed of Sienese painters and Bernardino di Betto. The sculptures contain the signatures of the greatest masters of history: Pisano, Donatello, Michelangelo, Bernini. The main circular stained glass window is the work of Duccio di Buoninsegna. Other important places inside the cathedral are the Piccolomini Altar, built by Andrea Bregno with Carrara marble, and the Piccolomini Bookshop, frescoed by Pinturicchio.