The Castel Sant'Angelo is a very tall cylindrical building in Rome that was initially built by the Roman Emperor Hadrian as a mausoleum for himself and his very large family. The building was a magnificent fortress and a gorgeous castle for over a thousand years but is now a museum. Originally, Castel Sant' Angelo was a decorated cylinder with a garden top. Hadrian's ashes were placed there after he died with the ashes of his wife Sabina. Following this, the remains of succeeding emperors were also put there and urns were probably placed in what is now a treasury room deep within the Castel Sant' Angelo.

In the year 401 A.D., the mausoleum was converted into a military fortress. During the siege by the Goths in 537 A.D., the bronze and stone statuary there were thrown down upon the attackers creating an historical event. The popes later converted the structure into a castle and specifically, Pope Nicholas III connected the castle to St. Peter's Basilica with a fortified corridor called the Passetto di Borgo. As a prison, Castel Sant' Angelo was also the setting of Giacomo Puccini's Tosca. This is the place from where the namesake of the opera leapt to her death.