The Diocesan Museum of Fermo is located in the historic center of the city next to the Metropolitan Cathedral Basilica. The Museum was inaugurated in 2004 and was strongly desired and followed in its realization by Archbishop Mons. Cleto Bellucci. Of great interest is the Treasure Room, so named because it houses the most precious objects of the Cathedral's Treasury and is the first room of the Diocesan Museum. Here we find the beautiful Missal de Firmonibus, a manuscript illuminated by Giovanni di Ugolino da Milano in 1436 commissioned by Giovanni De Firmonibus from whom it takes its name. This manuscript, an extraordinary example of Gothic art, contains thirty-one illuminated initials, decorated or historiated, two pages with large friezes and marginal miniatures, two full-page illustrations. The most famous page is certainly that of the Procession, where the historic procession in honor of the Assumption is depicted. The Stauroteca, a reliquary cross donated by Francesco Todeschini Piccolomini, future Pius III, in 1503, surely its creation is much older and of Venetian manufacture, for the filigree decoration. In the terminations of the arms, miniatures are inserted representing on the recto the protagonists of the Crucifixion, on the verso the symbols of the Evangelists.