“Petrus apostolus et Paulus doctor gentium”: the words of this liturgical chant are introduced by a virtuosically drawn historiated initial. Its fantastical architecture takes its fluting, trophies of arms and ovolos from the art of antiquity. The belly of the letter forms an open window giving onto the palace bedroom where Saint Prosdocimus, a disciple of Saint Peter who became bishop of Padua, baptizes Vitalian, the “king” of the city, in the presence of his wife. According to the legend, this conversion to Christianity augured a happy event for the couple, namely the birth of a daughter, Justina, who would be canonized for her exemplary life. A Dispute of Saint Justina and a Death of Saint Martin, held, respectively, by the Victoria and Albert Museum in London and the Musée Condé in Chantilly, both present striking similarities to this piece. In all likelihood, these three illuminations come from an antiphonary (a liturgical book of Gregorian plainsong) painted by the young Girolamo da Cremona for the monastery of Santa Giustina in Padua.