Erected as Hadrian’s Mausoleum on the right bank of the Tiber between 130 A.D. and 139 A.D., it received the remains of succeeding emperors up to Caracalla.
The original work was very different from the one you can see nowadays; its turning into a castle took place in the X century; in 1277 it became propriety of the Vatican, that joined it through the famous passetto to the Vatican walls.
The passetto is a long fortified corridor that allowed the passage of the pontiffs from the Vatican Palaces to the castle.
The name of Castel Sant’Angelo dates back to the XII century and originates from an ancient legend that tells the story of the plague in Rome in 590; according to this story the plague came to an end thanks to the apparition of an angel that alighted upon the mausoleum and made the gesture of replacing the sword in the sheath as a symbol of the accorded Grace.
To remember this event, not only the name of the monument was changed, but the statue in honor of the angel was put on the top.