Photographs of Rome's Castel Sant'Angelo, A Fairy-Tale Medieval Fortress

The most picturesque way to reach the castle is by crossing Pont Sant'Angelo bridge.

The bridge, and the hulking Renaissance fortress behind it, look the same today as they did in this 1905 watercolor....

...except that today the lady and her baby in the foreground would soon be mowed down by the ever-present Lungotevere traffic!

The origins of this amazing building go back to 135AD, when Emperor Hadrian decided to build himself a tomb.

Like Augustus before him, he selected a site on the green and shady banks of the Tiber River. The mausoleum and the bridge which gave access to it were not finished when the emperor died in 138AD, so Antoninus Pius completed them the next year and transferred Hadrian's ashes from their temporary burial place. A grand circular mole nearly 1000 meters in circumference, the mausoleum was faced with blocks of Parian marble and supported a cone of earth covered with evergreens, like the mausoleum of Augustus across the river.

Today all that is visible of the ancient work are the blocks of local peperino stone which once supported the outer casing.

Nothing was known of the internal layout until 1825, when the principal door was discovered in the middle of the square basement facing the bridge. It opened onto a spiral ramp, which still exists today, descending to the passageway which led to the graves of Hadrian and succeeding emperors up to Caracalla in 217AD.

In 271AD, the Aurelian Wall was added to fortify the mausoleum's strategic southern flank. The building's conversion into a military fortess was completed in 401 by Emperor Flavius Augustus Honorius.

Almost immediately, in 410, Alaric's Visigoths carried out the Sack of Rome. This was the first time in 800 years that Rome had fallen to a foreign enemy, and the city was decimated. Looters scattered the Imperial urns and ashes in the river. A century later in 537, the Goths repeated the outrage, and the defending garrison was forced to hurl the original decorative bronze and stone statuary down from the battlements upon the assailants. They might have viewed the ancient bridge through a peephole.

53 years later, Rome was besieged by a different enemy: the plague. Pope Gregory Great arranged for forty processions to march through the city towards the mausoleum. Citizens dropped to the pavement as they marched, felled by the pestilence. When the surviving population of Rome arrived at the bridge, legend holds that the pope saw Archangel Michael standing on the summit of what was left of the tomb, sheathing his sword. The plague ended soon thereafter, a chapel was erected on the spot and the place was rebaptised Castle of the Angel Saint.

As time went on, a bona fide Renaissance castle was eventually erected atop the ruins of the mausoleum.

In the 14th century, Pope Nicholas III connected the castle to St. Peter's Basilica by a covered fortified corridor called the Passetto di Borgo. St. Peter's looked different back then, but the Passetto didn't!

During the last great Sack of Rome in 1527, Pope Clement VII used the Passetto to reach sanctuary in the fortress. When the Pope saw this view of the castle, he knew he was safe.

Behind him, the darkness of foreign invasion closed in on the Passetto and St. Peter's beyond it.

Benvenuto Cellini was a prisoner in the castle at the time. He describes strolling the ramparts and shooting enemy soldiers during the fierce battle with Charles V's Landsknecht.

The castle's garrison made use of the cannons you can still see today.

The popes also used Sant'Angelo as a prison; Giordano Bruno, for example, was incarcerated there for six years before being burnt at the stake as a heretic in Campo de' Fiori.

Executions were carried out in the small piazza atop the ramparts.

As a prison, it was also the setting for the third act of Giacomo Puccini's Tosca, and it was from these ramparts that the tragic heroine leapt to her death.

One imagines that civil servants performing their routine duties in the offices next door would have seen her as she plunged past centuries of history.

Countless popes have left their mark on the castle over the centuries, from Gregory the Great to Nicholas V, whose 15th-century reign was too short for him to fulfill his dream of rebuilding the castle and surrounding Borgo, but not too brief to prevent him from affixing his coat of arms to the northern turret.

The great Spanish Pope Alexander VI (who was seated on St. Peter's throne the day Cristoforo Colombo discovered the New World for his Spanish patrons Isabelle and Ferdinand) made sure his papal coat of arms took center stage, right above the main entrance.