Legend holds that the Archangel Michael appeared atop the mausoleum, sheathing his sword as a sign of the end of the plague of 590, thus lending the castle its present name.
A less charitable yet more relevant elaboration of the legend, given the militant disposition of this archangel, was heard by the 15th-century traveler who saw an angel statue on the castle roof. He recounts that during a prolonged season of the plague, Pope Gregory I heard that the populace, even Christians, had begun revering a pagan idol at the church of Santa Agata in Suburra. A vision urged the pope to lead a procession to the church. Upon arriving, the idol miraculously fell apart with a clap of thunder. Returning to St Peter's by the Aelian Bridge, the pope had another vision of an angel atop the castle, wiping the blood from his sword on his mantle, and then sheathing it. While the pope interpreted this as a sign that God was appeased, this did not prevent Gregory from destroying more sites of pagan worship in Rome.
The popes converted the structure into a castle, beginning in the 14th century; Pope Nicholas III connected the castle to St Peter's Basilica by a covered fortified corridor called the Passetto di Borgo. The fortress was the refuge of Pope Clement VII from the siege of Charles V's Landsknechte during the Sack of Rome (1527), in which Benvenuto Cellini describes strolling the ramparts and shooting enemy soldiers.
Michael is an archangel in Judaism, Christianity, and Islam. In Roman Catholic, Eastern Orthodox, Anglican, and Lutheran systems of faith, he is called "Saint Michael the Archangel" and "Saint Michael". In the Oriental Orthodox and Eastern Orthodox religions, he is called "Saint Michael the Taxiarch".
Michael is mentioned three times in the Book of Daniel. The idea that Michael was the advocate of the Jews became so prevalent that, in spite of the rabbinical prohibition against appealing to angels as intermediaries between God and his people, Michael came to occupy a certain place in the Jewish liturgy.
In the New Testament Michael leads God's armies against Satan's forces in the Book of Revelation, where during the war in heaven he defeats Satan. In the Epistle of Jude Michael is specifically referred to as "the archangel Michael". Catholic sanctuaries to Michael appeared in the 4th century, when he was first seen as a healing angel, and then over time as a protector and the leader of the army of God against the forces of evil.
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