Originally, the 2nd-century Castel Sant’Angelo, or Castle of the Holy Angel, was a mausoleum for emperor Hadrian. After archangel Michael appeared here in 590 and ended a plague, pope Pius II had a large bronze statue of the angels placed on top of the castle. The Castle of the Holy Angel was part of Rome’s defences and offered a place where popes could shelter, as the Vatican was connected to it by a tunnel.