Castel Sant'Angelo, also known as the Mausoleum of Hadrian, is a towering cylindrical building in Parco Adriano, Rome, Italy. The history of this architectural masterpiece dates back to 139 AD when Emperor Hadrian commissioned it as a mausoleum for himself and his family. It was completed in 139 AD under the rule of his successor, Antoninus Pius. The name "Castel Sant'Angelo" was derived from a vision Pope Gregory the Great had in 590 AD. During a great plague, the Pope saw an angel sheathing its sword atop the castle, indicating the end of the plague. Hence, it was named "Castle of the Holy Angel," or "Castel Sant'Angelo." This castle has witnessed the transformation of Rome and served various purposes throughout history. It was used as a fortress and refuge by Popes in times of danger, a prison, and even a place of execution during the Middle Ages. It was only in 1901 that it was decommissioned and turned into a museum. The exterior of Castel Sant'Angelo is a sight to behold with its robust and imposing structure. It is divided into five floors. The second floor houses the historical prison cells, while the upper floors lead to the military and papal apartments, which are adorned with Renaissance frescos. The interior is equally impressive. The famous spiral ramp, which extends up to the second floor, is a striking architectural feature. It was designed to allow easy access for the carts carrying the imperial funerary that were to be deposited in the mausoleum. Moreover, the Papal apartments, decorated by artists like Pinturicchio and Perino del Vaga, are richly adorned with beautiful frescoes. The castle's terrace offers a breathtaking panorama of Rome. It is adorned by the bronze statue of Archangel Michael, symbolizing the legend of the angel that appeared to Pope Gregory the Great. Castel Sant'Angelo is not just a historic monument; it is a symbol of continuity, from the Roman Empire to today's modern Rome. It is an iconic monument that has survived through different epochs, bearing witness to the evolution of Rome's history.