Castel Sant'Angelo
Hadrian commissioned this cylindrical mausoleum as a dynastic burial monument, completed in 139 AD — one of the most ambitious building projects of the Roman Empire.
The internal spiral ramp leading to the burial chamber is a feat of Roman engineering still visible today, and it tells you how seriously Hadrian took the idea of an eternal monument.
The mausoleum was converted into a military fortress by the late Roman period and later became the primary refuge of the medieval and Renaissance papacy, illustrating how Christian Rome literally occupied the infrastructure of imperial Rome.
