 Guastalla formed part of the diocese of Reggio until 1471, when the Collegiate Church of S. Peter of Guastalla was declared to be "nullius dioecesis" (of no diocese) and was territorially detached from the jurisdiction of the bishop of Reggio Emilia.On 5 November 1585 Pope Sixtus V promoted it to the status of a secular territorial abbey "nullius dioecesis" (belonging to no diocese), as the abbey of San Pietro Apostolo di Guastalla"'.The eleventh Abbot Ordinary of Guastalla, Francesco Maria Scutellari of Parma, was also titular bishop of Joppa (Palestine).