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

Legend has it that this bronze orb, which sat atop an ancient Egyptian obelisk, once held the ashes of Julius Caesar.

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

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

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

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

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.

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

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

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

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.

2300-year-old Roman road connecting the empire.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

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

This historic boathouse was constructed using salvaged lumber from burned barns.

A tribute to the pop culture icon overlooks this Washington D.C. intersection.

An amazing example of early-20th-century architecture, this church features marble transported from Utah.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

Was there a small "backpack nuke" hidden in the attic? JFK apparently thought so.

This nine-story building is the oldest standing skyscraper in D.C.

An overlooked memorial honoring the local Washington residents who died in World War I.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.