The Mausoleum was used as a dynastic tomb at least until the time of Caracalla, in the early 3rd century AD. Its decline began in 537 AD during the siege of the Goths led by Vitiges: the Romans barricaded themselves in the Mausoleum under the leadership of General Belisarius, and to defend themselves, they smashed its statues and marbles to pieces and used them as projectiles. Gradually, the Mausoleum was stripped of all its most precious materials, and the travertine was used to pave Rome's streets and squares.
In 864, the Mausoleum was included in the new city walls—the Leonine Walls—built by Pope Leo IV to protect St. Peter's Basilica and the Borgo from Saracen attacks and looting. In the 15th century it was transformed into a fortress, with a moat dug around the Mausoleum's circular tower and a drawbridge added.
Whoever controlled Castel Sant'Angelo controlled the entire city, so during the Middle Ages and the Renaissance, what little remained of the original Roman mausoleum was incorporated into new defensive structures that turned it into an impregnable fortress and, at the same time, a splendid papal residence decorated by the finest artists of the time. Popes often took refuge there during sieges, including that of the Landsknechts in 1527. The Hall of the Burial Urns was transformed into a casemate defended by cannons.
The Aelius Bridge originally had eight arches, three larger central ones and five others of decreasing size, to adapt to the varying water levels of the river and prevent flooding; an extraordinary example of Roman mastery in the field of hydraulics.
According to the legend, in 590 AD the Archangel Michael appeared to Pope St. Gregory the Great, who was leading a penitential procession across the bridge: he announced the end of the plague, sheathing his sword. From that moment on, the Mausoleum and the bridge changed their names: Castel Sant'Angelo and Ponte Sant'Angelo.
In the 17th century, Gian Lorenzo Bernini designed the new parapets of the Aelius Bridge and the ten statues of angels that still adorn it.
During the Middle Ages and the Renaissance, the bridge's smaller arches had been walled up several times to build hanging gardens: this transformed the bridge itself into a veritable dam, diminished the river's flow, and caused devastating floods.
Therefore at the end of the 19th century it was decided to raise the river banks by building the Lungotevere embankments. All later additions were demolished, resulting in an extraordinary discovery: the original smaller arches of the Pons Aelius, until then hidden by modern masonry, were perfectly preserved; even the paving, the sidewalks, and the access ramp to the Mausoleum itself, with its threshold and enclosure were found.
In our book, «Castel Sant'Angelo. Mausoleum of Hadrian. Architecture & Light» (also in English edition) we publish rare photographs of that discovery and tell its sad story. Unfortunately, the original ramps of the Aelius Bridge were mercilessly demolished along with everything else, so as not to interrupt the construction of the Lungotevere, despite the desperate pleas of archaeologist Rodolfo Lanciani.
After being transformed into a prison and barracks, the Mausoleum was restored in the late 19th century and transformed into the present Museum, one of the most beautiful and interesting in Rome.
Meanwhile, the Aelius Bridge, completely rebuilt, is still decorated with statues of Angels with the symbols of the Passion designed by Gian Lorenzo Bernini, and those of the Apostles Peter and Paul.