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.