In the upper curve of the apse is a magnificent fresco, representing the Adoration of the Mystic Lamb. The fresco shows the scene described in the book of Revelation in which the Lamb that was slain from the beginning is enthroned, encompassed by angels offering incense, which are the prayers of the Saints, and by the twenty-four Eiders, and prophetic emblem of the Great Christian Sacrifice. The apse fresco was painted by Giovanni Battista Gaulli, in 1679.