The forces of John XII, not yet 26 years of age, had been defeated in the war against
Pandolfo Testa di Ferro of
Capua, and at the same time many strongholds in the
Papal States were occupied by
Berengar of Ivrea, effectively if not completely legally King of Italy, and his son Adalbert. In this dilemma the Pope had recourse to Otto who reappeared in Italy at the head of a powerful army, as he had in the previous decade, now ostensibly as a papal
champion. Berengar, however, did not risk an encounter, but retired to his fortified castles. Thus, without conclusive military encounters, on January 31, 962, Otto reached Rome. He took an oath to recognize John as Pope and ruler of Rome; to issue no decrees without the Pope's consent; and, in case he should deliver the command in Italy to anyone else, to exact from such person an oath to defend to the utmost of his ability the Pope and the Patrimony of Peter. The Pope for his part swore to keep faith with Otto and to conclude no alliance with Berengar and Adalbert. Subsequently, on February 2 Otto was solemnly crowned
Holy Roman Emperor by the Pope. Ten days later at a Roman synod, John, at Otto's desire, founded the
Archbishopric of Magdeburg and the
Bishopric of Merseburg, bestowed the pallium on the
Archbishop of Salzburg and
Archbishop of Trier, and confirmed the appointment of
Rather as
Bishop of Verona. The next day, the emperor issued a decree, the famous
Diploma Ottonianum, in which he confirmed the Roman Church in its possessions, particularly those granted by the
Donation of Pepin and by Charlemagne, and provided at the same time that in the future, the Popes should be elected in canonical form, though their consecration was to take place only after the necessary pledges had been given to the emperor or his ambassadors. In essence, the Emperor was to be the guarantor of Papal independence, but to retain the right to confirm Papal elections. Historians debate, in terms of power and prestige, whether the
Diploma Ottonianum was a prestigious advantage for the papacy or a political triumph for the emperor. On 14 February the emperor marched out of Rome with his army to resume the war against Berengar and Adalbert. The Pope now quickly changed his mind, while Otto on his part pressed his imperial authority to excessive limits, and the brief alliance dissolved in wrangling. John sent envoys to the
Magyars and the
Byzantine Empire to form a league against Otto, who returned to Rome in November 963, and convened a synod of bishops that deposed John and crowned
Pope Leo VIII, a layman, as pope. The authenticity of the contents of this much-discussed document seems certain, even though, like other 10th century documents, the extant document seems to be only a duplicate of the original (Sickel,
Das Privilegium Ottos I, für die römische Kirche, Innsbruck, 1883). == Later developments and repeal ==