Castel Sant'Angelo, Rome During its many years of existence, the building functioned first as a mausoleum, then became part of the city wall and later was turned into a fortress before it functioned as a papal residence and finally as a barracks and military prison. It is currently a national museum. Hadrian's Mausoleum The Castel Sant'Angelo was originally built by Emperor Hadrian as a mausoleum. Construction started in 123 A.D. and was finished in 139 A.D., during the reign of Hadrian's successor, Antoninus Pius. The building consisted of a square 89m (292ft) wide base on which a cylindrical colonnaded drum with a diameter of 64m was constructed. On the drum was an earthen tumulus topped by a quadriga with Hadrian's statue. The mausoleum was connected to the city at the other side of the river by a newly constructed bridge, the Pons Aelius. The bridge is now known as the Pont Sant'Angelo. Its many statues were added later during the Renaissance. The mausoleum housed the remains of Hadrian and his successors up to Caracalla. Papal Refuge Between 270 and 275 A.D., during the construction of the Aurelian walls, Hadrian's mausoleum was fortified and incorporated in the Aurelian Wall around Rome. From that point on the building was slowly turned into a fortress and in 1277 it was acquired by the papacy who used the building as a refuge in case of danger. A secret corridor, known as the Passetto di Borgo, connects the Castel Sant'Angelo with the Vatican. The corridor was used by Pope Clement VII and his Swiss Guards to take refuge from Charles de Bourbon's army during the sack of Rome in 1527. Interior But even in this fortress, the pontiffs made sure they were well housed. The papal apartments in the Castel Sant'Angelo feature beautiful rooms decorated with many frescoes. Below the apartments are several floors which include prisons and even a torture chamber. A spiraling corridor, part of the original mausoleum, leads to the bottom of the building. Angel Statue At the top of the fortress, looking over the panoramic terrace, is a statue of an angel, built by the 18th century Flemish sculptor Pieter Verschaffelt. The bronze statue replaced an earlier, marble version.turkeyarena.com The statue depicts the angel who, according to legend, appeared on top of the fortress in the year 590 and miraculously ended the severe plague that had infested the city of Rome. After the event, the building was renamed Castel Sant'Angelo.