Known as Hadrian's Tomb, the Castel Sant'Angelo is a fortress located on the right bank of the Tiber, a short distance from the Vatican City. Construction of the building began in the year 135 under the direction of the Emperor Hadrian, who intended to use it as mausoleum for himself and his family. It was finished in the year 139 and a short time later, it became a military building, which in the year 403 would be integrated to the Aurelian Walls.

In the year 590, while a great epidemic of plague devastated the city, the Pope Gregory I had a vision of Saint Michael the Archangel on top of the castle, announcing the end of the epidemic. In memory of the apparition the building is crowned with a statue of an angel.

In the year 1277 an 800 metre fortified corridor was built that connected the castle with the Vatican City so that the Pope could escape in the event that he were in danger. During the sieges that occurred in Rome during 1527, the Pope Clement VII used the fortress as a refuge.