On the foundations of a church dedicated to the martyrs St Firmanus and St Rustico, the Benedictine monks built San Fermo Maggiore in the 11C, designed as two distinct superimposed churches. The lower church represents a rare example of a primitive Romanesque church, whose three naves are separated by pillars adorned with frescoes. The upper building houses the fresco of the Annunciation by Pisanello (1426), which frames the Brenzoni mausoleum (1430), a masterpiece by the Tuscan Nanni di Bartolo.