This observation comes from Giulia Maria Anglani, who guided at the catacombs for around ten years.

“Underground, someone would ask whether the Romans lived down here. Not as a joke — as a real question. They had been descending stairs all week, in churches and basements, and had drawn the obvious conclusion.”

The reasoning is sound. In Rome you go down to reach antiquity, over and over, and after a few days it begins to look like a rule about how the city was built.

It is not.

It is a rule about what happened afterwards.

The Romans Lived at Street Level

Their street level. It is roughly where you now find basements, cellars, archaeological areas and the lower levels of later buildings.

Rome’s ground level changed over centuries. Flood deposits, collapsed buildings, demolition material, rebuilding and the deliberate filling of earlier structures gradually created new surfaces above older ones.

Nothing had to “sink”.

The city repeatedly built above what already existed.

Where You Can See the City’s Layers

San Clemente, only a short walk from the Colosseum, is one of the clearest places in Rome to understand this process.

The church visible today dates largely from the early twelfth century. Beneath it survives an earlier Christian basilica. Deeper still are Roman structures dating back to the Imperial period, including a mithraeum and spaces belonging to an earlier urban landscape.

Different phases of Rome occupy different vertical levels.

What appears to the modern visitor as an underground archaeological site was once architecture at, or close to, the surface of the city that existed at that time.

This Happened Across Rome

San Clemente is one particularly dramatic example, but the phenomenon is visible throughout the historic city.

Beneath medieval and Renaissance buildings around Campo de’ Fiori, the Tiber and the Regola district, Roman structures survive below the present street level.

The archaeological remains beneath San Paolo alla Regola are a striking example.

What is underground today was not originally built underground.

The buildings survived because the city continued above them.

The Part That Surprises People

Archaeological layers are often imagined as cities that were mysteriously swallowed by the ground.

Rome usually tells a more practical story.

Buildings were abandoned, modified, demolished or deliberately filled. New structures reused old walls. Floors were raised. Streets changed level. Foundations incorporated what had already been there.

Over long periods of time, yesterday’s ground floor could become tomorrow’s basement.

What Happened at San Clemente

The earlier Christian basilica beneath the present church was eventually filled and incorporated into the construction history of the site.

In the nineteenth century, Dominican excavations led by Joseph Mullooly brought the earlier structures back to light.

The result allows visitors today to move physically through different periods of Rome simply by descending from one level to another.

What to Look At

When visiting an underground archaeological site in Rome, stop thinking of it as an underground world for a moment.

Look at doors, thresholds, pavements and windows.

Look at the orientation of corridors and the height of ancient floors. Try to reconstruct where daylight would once have entered and where streets would have continued outside the surviving walls.

The decisive change in perspective is simple: imagine removing everything built above you.

Suddenly the basement becomes a street-level building again.

The Romans did not live underground. They lived here, at this level, in the open air. Much of the Rome above them arrived later.