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

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

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

An ancient Roman temple first dedicated to an emperor's wife is now a church.

Ancient ruins hidden underneath a modern luxury hotel.

An abandoned 17th-century baroque hunting lodge with a wonderfully strange architectural plan.

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

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

Roman politician Herodes Atticus built this nymphaeum to honor his wife, whom he may have murdered.

These hut foundations are believed to be the residence of Romulus, founder of Rome.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

In the early Roman Empire, people deemed traitors and criminals were tossed to their deaths from this rock.

One of Rome's most picturesque and original bridges was also a popular choice for Grand Tour artists.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

Rome is now home to a stunning food museum and library.

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

The mystic whose incorrupt corpse still attracts the faithful.

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

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

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.

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

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

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