The patron of Petriolo is Saint Mark, celebrated on 25 April.
In the Santuario della Madonna della Misericordia the wooden statue of the Madonna by Giovanni Antonio Aquilano (16th century) stands out; it was placed in 1525 in the Chiesa di Santa Maria in Piazza, later the church of the Madonna della Misericordia, following a miraculous event; next to the sanctuary stands the Museo dei legni processionali «Monsignor Marcello Manfroni» (museum of processional wooden objects).
