A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

A massive marble foot is tucked away in a small alley near the Pantheon.

Its interior is adorned with some of the best examples of early Christian mosaics.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

Charles Dickens was not a fan of the ghastly wall dressings in this 6th century church.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

This is the oldest Roman-made bridge in the city still existing in its original state.

Ancient ruins hidden underneath a modern luxury hotel.

This curious, round temple is the oldest still-standing marble building in Rome.

A modern sliver of architecture in Roma.

This ancient market is often referred to as the oldest shopping mall in the world.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

One of seven Jewish catacombs in Rome and one of only two open to the public.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

A Nesting Doll of Churches.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

In Rome’s Jewish ghetto, a 200-year-old bakery still makes the neighborhood’s historic sweets.