This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

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

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

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

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

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

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

This hydrochronometer was invented by a Dominican monk and is a prime feature in this garden.

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

The ruins of an abbey believed to have been founded by Charlemagne in the 9th century.

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

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

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

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

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

Ancient ruins hidden underneath a modern luxury hotel.

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

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.

A huge enchanting public park just outside the ancient walls of Rome.

An Italian ghost town that fought obscurity, until a mysterious illness brought it to its knees.

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

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