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

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

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

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

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

This statue is the only female representation of Rome's "talking statues."

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

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

A sculpture serving as an homage to Pope John Paul II.

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

Nicknamed “The Mushroom,” this unique water tower has been featured in several iconic movie scenes.

A secret hatch containing two parchments was discovered in this statue over 40 years after its installation.

A freedman baker’s lavish tomb has a relief showing various stages of Roman bread making.

Believed to be the remains of the lost Temple of Minerva, this nymphaeum has been known by its misnomer to this day.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

A statue representing a lost Roman profession that was vandalized for centuries.

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

Plaques on its facade commemorate the Tiber's most destructive deluges.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A deep mark on the remains of a Roman temple, believed to be left by a legendary warrior.

An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

The Pope’s secret escape route.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.