It is the oldest religious building in Guastalla and one of the oldest in the province. Dating back, in its primitive form, before the X century, it is now dedicated to the Saint Apostles Peter and Paul.
Its consecration dates back to 997 by Pope Gregory V. It was the seat of a Synod in 1095, with the Pope of the I Crusade Urban II, and a Council in 1106 with Pasquale II. In over a thousand years of its history it underwent various transformations, which ended in 1931, when a radical restoration was carried out, which restored it to its current splendor. In the right aisle there is a Madonna of fine work of the Modenese artist Guido Mazzoni, active in the mid-fifteenth century and estimated as the greatest Emilian sculptor of the time. In the left aisle there is a wooden Crucifix, polychrome, datable to the sixteenth century.