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There was a count in northern Italy named Berengar of Ivrea, who declared himself king. In about 860, Berengar invaded the Papal States, which caused Pope John XII to appeal to Otto, who was King of Germany and had already taken the title King of Lombardy. Otto helped the pope, who crowned him emperor of the Holy Roman Empire in return. As it happens, though Pope John XII and Otto I were pledged to support each other, they almost immediately became enemies. The pope entered into multiple conspiracies to depose Otto, and Otto attempted, with somewhat more success, to depose the pope.
The creation of the Holy Roman Empire restored the alliance between the pope and the emperor which had been established between Pope Leo III and Charlemagne. Pope John XII and Otto signed a document which declared the pope was the head of the church and Otto was the secular protector of the church.
Pope John XII rewarded Otto I By Crowning Him Emperor of The Romans.
Otto I got declared the Roman Emperor because he helped the Pope when he was struggling so the pope declared him the Roman Empire.
The Swiss Guard protects the pope.
The Swiss Guards are the most visible body guards of the pope.
Otto IV
otto I
When Otto I freed the Pope from the control of the Romans, he was named Holy Roman Emperor.
Sent troops to Italy to protect the pope
1945
The German guards were protecting the pope during the war