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

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

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

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

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

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

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

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

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

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

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

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

This large, circular tomb is the final resting place of the first emperor of Rome.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

The Pope’s secret escape route.

A Nesting Doll of Churches.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Jesus' footprints and the first catacombs in the world.

The final resting place of the poets Shelley and Keats.

2300-year-old Roman road connecting the empire.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The yawning maw of this pagan visage is said to bite off the hands of liars.