[1] On 21 October 1106, Pope Paschal II, at the Council of Guastalla, removed the dioceses of Emilia from the metropolitanate of Ravenna, and made them directly dependent upon the Holy See (papacy).

This action was in punishment for the schism carried on by Archbishop Wibert of Ravenna (Antipope Clement III), in concert with the Emperor Henry IV.

[4] Bishop Arduinus of Piacenza (1119?–1147), however, resisted efforts of the popes and the Archbishop of Ravenna to return his diocese to suffragan status.

[5] On 29 March 1148, Pope Eugene III wrote to Archbishop Moyses of Ravenna that he had approved the election of Bishop Joannes of Piacenza.

After resisting for more than two years, Giovanni finally submitted to the Pope's order, and was consecrated by the Archbishop of Ravenna on 3 July 1151.

They solicited the intervention of Abbot Peter the Venerable of Cluny, informing him of their point of view, that their metropolitan was the pope, not the Archbishops of Aquileia or Ravenna.

Piacenza was made a suffragan of the Archdiocese of Bologna by Pope Gregory XIII in the bull Universi orbis of 10 December 1582.

On 30 March 1818, Pope Pius VII removed the same three dioceses from the jurisdiction of the metropolitan Archdiocese of Genoa, and made them directly dependent upon the Holy See.

[12][13] An early martyr, St. Antonius (or Antoninus, as the diocese prefers), is said to have belonged to the Theban Legion, and to have suffered martyrdom at Piacenza in the second or third century.

He has no "Passion", however, and the ninth century document that makes him a member of the Theban legion is pieno di favole ('full of fables').

In 865, after twenty-five years of service in Piacenza, Bishop Soffredus (Seufredus) found himself driven from his office by the treachery of his own nephew, the deacon Paulus.

Nonetheless, on the death of Soffredus in 870, Paulus, who had evidently been restored to favor and was serving as Archdeacon of Piacenza, was elected bishop in his place.

[19] During the last six years of his administration, Bishop Sigulfus (951–988) enjoyed the services of a coadjutor-bishop, Johannes Philagathos, who, thanks to the patronage of the Empress Theophano, was also Abbot of the Monastery of Nonantola and tutor of the child who would become the Emperor Otto III.

[20] The diocese of Piacenza had been detached from the ecclesiastical province of Ravenna, through the influence of the Regent Theophano and with the consent of Pope John XV, and erected into an archdiocese directly dependent upon the Papacy.

[27] After little more than a year in the diocese, he was again appointed papal Nuncio to Spain on 20 September 1583, and, due to a serious illness at the end of the mission, which incapacitated him for five months in Barcelona, he did not return to Piacenza until June 1584.

His tenure was not long, however, for the Pope appointed him Nuncio to the Holy Roman Emperor Rudolf II in Vienna on 18 January 1586, a post which he held until 28 May 1587.

[31] A beneficial side-effect of the Bishop's frequent absences was that Piacenza did not fall under subordination (suffragan status) to any of the neighboring metropolitanates.

Cardinal Carlo Borromeo of Milan was especially enthusiastic for Tridentine reform, and held frequent diocesan and provincial synods, inviting the bishops of Piacenza to the latter.

Among other things, it ordered clerici concubinarii (clergy with wives) to leave their houses within eight days of the publication of the synodical decrees, and not to take their children with them.