Castel Sant'angelo (Sant'angelo), a powerful block which still dominates the panorama of Rome, originally served as the burial place of the emperors and was turned into a fortress only in the middle ages. The castle is also called the Mausoleum of Hadrian. To put together this majestic monument to the Champs de Mars, was constructed the Bridge of Sant'angelo. It consists of three huge Central arch and two inclined platforms supported by three arches from the right Bank and two from the left.

Diagram of the construction of the mausoleum is included in the building of the castle of Sant'angelo in the middle ages, largely remained unchanged. The building is on a huge four-cornered base, the length of each side of which is 89 meters and a height of 15 meters. On this base is mounted a cylindrical drum with a height of 21 meters, surrounded by radial walls. On top of this drum is poured huge earthen hill, planted with trees, and around the edge of the marble statues. The exterior is lined with the moon stone (marble) with signs attached around the entire circumference of the wall, which indicated the names and titles of those who were buried inside the mausoleum. The burial chamber, located in the heart of a massive drum, is square in shape with three rectangular niches. In this room were placed the urn containing the ashes of the emperors.

In 403, the Emperor Honorius turned this building into a Bastion of the defensive walls of Aurelian. Becoming a fortress, it is in 537 year was under siege from the ready under the leadership of Mitiga. His transformation into the castle occurred in the tenth century. Today the castle is a strong fortress on a square base with four round towers at the corners, bearing the names of the apostles : St. Matthew, St. John, St. Mark and St Luke. During the pontificate of Benedict IX on the basis of the installed cylindrical body, repeating the scheme for the construction of the mausoleum of Hadrian. Further changes were introduced to the castle during the reign of popes Alexander VI and Julius II. At last at the top of the castle, as the framing of the apartments of the Pope, was built loggia.

Upstairs there is a viewing terrace over which hovers an angel, which gave the name to the castle, which on their wings, according to legend, brought the saving deliverance of Rome from a terrible plague was raging in the pontificate of Gregory the Great. Inside the castle are now a national military Museum and Museum of art.