A legend has it that Gregory the Great (or Pope Saint Gregory I) had a vision of Michael the Archangel appearing there, to mark the end of the plague. The angel is represented by a bronze statue, a replica of Giacomo della Porta’s original. The castle’s construction was begun by Hadrianus (also written Adrianus) who desired to build a mausoleum. Indeed served the castle as a mausoleum until the time of Septimius Severus, then at the time of Aurelianus’s rule in 3th century, the emperor had it transformed into a fortress, circling the monument within high walls bearing his name. Theodoric, King of the Visigoths, made the place a prison. And in the 15th century, Antonio da Sangallo the Younger renovated it once again. The Castle of Saint Michael the Archangel is related to many dramatic episodes of Rome’s history. A secret corridor connects it to the Vatican.