The Oratorium Populi is decorated with layers of frescoes depicting images of Saints which, overlapping, create an historical-artistic palimpsest of great interest. The oldest figures (12th -13th century) observe the Byzantine iconography. Of this time is the Christ Pantocrator who, seated on an imperial throne typically oriental style, with his stern look, shows his omnipotence encircled by four cherubs. The similarities with artistic works of the same iconographic subject of the 12th century (Cathedral of Cefalù), help us to date this work to the Norman period. 

To the North of the apse there are some remains of a Crucifixion. On the following wall, several devotional acts have succeeded over the centuries, creating up to five layers of frescoes. The most frequent holy images, on this side, are related to the Virgin Mary.

The rocky septum which separates the two western spaces is decorated only on one side, where five icons are depicted, separated by red and white frames. On the western back wall we can see two images of the 15th and 16th century: a Christ the Wayfarer and St. Christopher. In the small north-west space was depicted a Deposition (17th century), which is nowadays kept at the Archaeological Museum of Lentini.