Mausoleum of Hadrian: The Origin of Castel Sant'Angelo in Rome

The Mausoleum of Hadrian is a monumental tomb built by the Roman emperor Hadrian on the right bank of the Tiber in Rome, begun around AD 134 and completed in 139, after his death. It held the ashes of emperors for nearly a century. Later fortified and rebuilt by the popes, it became Castel Sant’Angelo, one of the most recognisable landmarks of Rome.

Building the tomb

By the 130s the Mausoleum of Augustus on the Campus Martius was full. Hadrian chose a site across the river, in the gardens of the Ager Vaticanus, and in AD 134 dedicated a new bridge, the Pons Aelius, to link the tomb to the city. The bridge survives, much restored, as the Ponte Sant’Angelo. Its parapets now carry ten marble angels holding the instruments of Christ’s Passion, carved to designs by Gian Lorenzo Bernini and installed around 1669-1671 under Pope Clement IX, which turned the approach to the castle into a pilgrim route towards St Peter’s.

The tomb consisted of a square podium, roughly 89 metres on each side, faced with marble. On it stood a huge cylindrical drum about 64 metres in diameter, built of concrete and faced with travertine and marble. Its top probably carried earth planted with trees and a central structure crowned by a statue or a bronze chariot group; the exact appearance is uncertain. Inside, a spiral ramp, which still survives, led up to the burial chamber at the heart of the drum.

Hadrian died at Baiae in July AD 138 and was first buried at Puteoli. His successor, Antoninus Pius, completed the mausoleum and moved his ashes there in 139.

An imperial burial place

Hadrian and his wife Sabina, as well as his adopted heir Lucius Aelius Caesar, who died in 138, were buried in the tomb. Antoninus Pius, Marcus Aurelius, Lucius Verus, Commodus and Septimius Severus followed. Caracalla, who died in AD 217, is the last emperor known to have been interred. The urns and most of the inscriptions were lost when the building was looted.

From tomb to fortress

When the emperor Aurelian built new walls around Rome in the 270s (see Aurelian Walls), the mausoleum stood outside them. By the early 5th century it had been incorporated into the city’s defences as a bridgehead fort on the right bank.

During the Gothic War, in AD 537, Rome’s defenders under Belisarius held it against a Gothic assault. The historian Procopius reports that, running out of missiles, they broke up the tomb’s statues and hurled the pieces at the attackers.

The name comes from a legend about Pope Gregory the Great. During a plague in AD 590 he is said to have seen the Archangel Michael above the mausoleum, sheathing his sword to show that the epidemic would end. The story is first recorded centuries later, but it gave the castle its name, and statues of the angel have stood on top since the Middle Ages. The present bronze angel, by Peter Anton von Verschaffelt, dates from 1753.

The papal castle

In the Middle Ages Roman noble families fought for control of the fortress. From the late 13th and 14th centuries it passed firmly to the popes, who built apartments, bastions and storerooms on top of the Roman drum. Pope Nicholas III (1277-1280) is credited with the Passetto di Borgo, a fortified corridor on top of a wall linking the castle to the Vatican, later rebuilt.

The castle proved its worth during the Sack of Rome in 1527. Pope Clement VII fled along the Passetto and held out inside while mutinous imperial troops plundered the city. Later popes, especially Paul III, decorated rich apartments within the fortress.

The castle also served as a prison, holding political and religious prisoners over several centuries, among them the goldsmith and sculptor Benvenuto Cellini, who later described his escape. Its terrace is the setting for the final act of Puccini’s opera Tosca (1900).

Museum

After Italian unification the castle served as a barracks and military prison. Restored in the early 20th century, it became the Museo Nazionale di Castel Sant’Angelo, which displays the building’s history from Roman tomb to papal fortress.

Timeline

• AD 134: The Pons Aelius is dedicated; work on the mausoleum is under way.
• AD 138: Hadrian dies at Baiae.
• AD 139: Antoninus Pius completes the tomb and moves Hadrian’s ashes there.
• AD 217: Caracalla, the last emperor known to be buried there, dies.
• AD 537: Defenders hold the mausoleum against the Goths.
• AD 590: Traditional date of Gregory the Great’s vision of the angel.
• 1527: Clement VII takes refuge during the Sack of Rome.
• 1753: Verschaffelt’s bronze angel is placed on top.

Why it matters

Few buildings show Rome’s layered history so clearly. An emperor’s tomb became a fortress, a papal refuge, a prison and a museum, yet the Roman drum still forms its core.