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Papal politics

On 12 February 962, Emperor Otto I and Pope John XII called a synod in Rome to legalise their relationship. At the synod, Pope John XII approved Otto's long-desired Archdiocese of Magdeburg. The Emperor had planned the establishment of the archdiocese to commemorate his victory at the Battle of Lechfeld over the Hungarians and to further convert the local Slavs to Christianity. The Pope named the former royal monastery of St. Maurice as provisional center of the new archdiocese, and called upon the German archbishops for support.

The following day, Otto and John XII ratified the Diploma Ottonianum, confirming John XII as the spiritual head of the Church and Otto as its secular protector. In the Diploma, Otto acknowledged the earlier Donation of Pepin of 754 between Pepin the Short, King of the Franks and Pope Stephen II. Otto recognized John XII's secular control over the Papal States, and expanded the Pope's domain by the Exarchate of Ravenna, the Duchy of Spoleto, the Duchy of Benevento and several smaller possessions. Otto however didn't have the obligation to deliver military aid in case the territories would be conquered by others and despite this confirmed claim, Otto never ceded real control over those additional territories. The Diploma granted the clergy and people of Rome the exclusive right to elect the pontiff. The pope-elect was required to issue an oath of allegiance to the emperor before his confirmation as pope an agreement based on feudal law with the consequence that the emperor had power over the pope and not vice versa.

With the Diploma signed, the new Emperor marched against Berengar II to reconquer Italy. Being besieged at San Leo, Berengar II surrendered in 963. Upon the successful completion of Otto's campaign, John XII began to fear the Emperor's rising power in Italy and opened negotiations with Berengar II's son, Adalbert of Italy to depose Otto. The Pope also sent envoys to the Hungarians and the Byzantine Empire to join him and Adalbert in an alliance against the Emperor. Otto discovered the Pope's plot and, after defeating and imprisoning Berengar II, marched on Rome. John XII fled from Rome, and Otto, upon his arrival in Rome, summoned a council and deposed John XII as Pope, appointing Leo VIII as his successor.