COMACCHIO, Diocese of. - Episcopal see of Emilia, in the province of Ferrara, suffragan of Ravenna. Its origin has often been traced back to the 6th century, assigning as the first holder of the diocese the bishop Pacatian (502), who instead belongs to Imola. Likewise another anonymous bishop of 592 comes from a spurious diploma of Gregory the Great to Marinianus, bishop of Ravenna (Jaffé-Wattenbach, 1883 a.).
The first historically attested bishop of C. is Vincent, living in the 8th century, as attested by an epigraph existing in the cathedral of C., which calls him a contemporary of the archbishop of Ravenna Felix (708-724). Subsequently mention is made of Vitalis in a diploma of Charlemagne of 787; of Cyprian, who in 858 subscribed a constitution in favor of the monastery of Palazziola; of Stephen, appointed by John VIII and remembered in two diplomas of the same Pope to Count Berengar. As suffragans of Ravenna the bishops of C. often took part in the synods of the metropolitan see; thus, for example: Ursus (954), George (997), succeeded by John, of whom St. Peter Damian speaks, and who died as a penitent in the monastery of Pomposa. C. took part in the Guibertist schism (Clement III) under bishop Adalbert, who signed his acts with the date of the antipope. Likewise during the Western Schism C. was a field of contention among the popes struggling with one another.
The situation was normalized with the elevation to the throne of Martin V. The duchy of C. was first at the disposal of the popes; in the 10th century it was held by the empress Adelaide, after whose death Gregory V entrusted it to the archbishop of Ravenna Gerbert. In recent times it was the object of long disputes between the Holy See and Austria, and in the 18th century much ink was spilled over the rights of the Church and the Empire over the duchy.
Among the ancient abbeys of the territory of C. that exercised a notable influence on medieval Italian religious life, mention should be made of: S. Maria in Aula Regia (Benedictine), already flourishing in the 10th century, later fallen into neglect and restored in the 15th century by bishop Mainardino; S. Giacomo de Cella Volana and especially the abbey of Pomposa (v.), existing in 874, but of far more remote origins, often the object of imperial and royal privileges.
It had representative men such as Peter Damian and the musician Guido d'Arezzo. Having declined, in part because of the unhealthy climate, it was later converted into a secular provostry under Alexander VI and Innocent VIII.
The cathedral of C., dedicated to St. Cassian, was rebuilt by bishop Sigismondo Isei in 1659 and brought to completion by his successor Nicolò Arcani.
The diocese, in an area of 1600 sq km, counts 27 parishes, with a population of 73,000 inhabitants, all Catholics, 27 diocesan priests, and 10 regulars (1948).