Hadrian, the Roman emperor, originally built Castel Sant'Angelo as a tomb. The mausoleum for Hadrian and his successors was housed in this structure, which also served as their tomb. In fact, the engineering of the Augustus Tomb, which had been built a century earlier, served as the basis for the design and construction of Hadrian's mausoleum. Under the direction of the emperor himself, the building of Hadrian's tomb started in 123 AD and was finished in 139 AD by Antoninus Pius, Hadrian's successor. A 64 meters wide cylindrical colonnaded drum was constructed above a 292 feet wide square base that served as the mausoleum's foundation. A tumulus that had a statue of Hadrian on a chariot perched atop it entirely around the drum.

Hadrian's Mausoleum was fortified between 270 and 275 AD with the construction of the Aurelian Wall. The tomb had changed its name at this point to Castel Sant'Angelo, so from this point forward the structure was progressively transformed into a fort. The papacy took control of this citadel in 1277, and the pope utilized it as a fortified haven whenever he was in danger.A covert bridge known as Passetto di Borgo connected Castel Sant'Angelo to Vatican City. In order to evade Charles de Bourbon's troops in 1527, Pope Clement VII and his Swiss Guards utilized this route as cover. The architecture of the Papal Refuge is a must-watch as it showcases how a tomb became a fort representing a cover for the guards to avoid the troops.

The Passetto di Borgo, or Passetto, is another name for Er Coridore De Borgo (the Corridor of Borgo), as it was known to the Romans of papal Rome. It is comparable to the elevated and fortified portion of the Vatican Walls that extends from the Apostolic Palace of the Vatican, commencing from behind the colonnade of Bernini, through via dei Corridori and via Borgo Sant'Angelo, and terminates in Castel Sant'Angelo.

To defend the military camp that the barbarian Totila established in this region of the city about the year 547, it was a component of a defensive system that stretched from the base of the Vatican Hill to the Mausoleum of Hadrian. The structure, which has an irregular form and a low elevation, was constructed with large, roughly squared blocks and is still partially visible next to Porta Castello. To safeguard the St. Peter's Basilica and the surrounding structures, Pope Leo IV (847-855) constructed a city wall that was about 5 meters high and included a promenade. Wherever feasible, he made use of them which was before architecture that would eventually be used to build the Passetto as we understand it to establish it.

Do Checkout: Best Places To Visit Near Castel Sant Angelo

Ponte Sant’Angelo originally known as Pons Aelius, Ponte Sant'Angelo was constructed in 136 AD by the Roman emperor Aelius Hadrian to link the city to the entrance to his tomb, the modern Castel Sant'Angelo. Over the years, this bridge was witness to a number of significant occurrences. Traffic across the bridge had to be controlled in the fourteenth century during the first Holy Year declared by Pope Boniface the Eighth due to the enormous numbers of pilgrims. Dante Alighieri claims that two opposing pathways separated by a row of ticket booths were made on the bridge and used as a shortcut from the city to Saint Peter's.

Instead, numerous people drowned in the river during the Holy Year of 1450 when the bridge's rails collapsed as a result of an accident caused by the white mule carrying Pope Nicholas the Fifth. The bridge and the area in front of it served as the scaffold exhibition.

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