But it is Christianity that has bestowed the greatest number of stories of miracles and mystery in Rome. There are relics of saints and clues to practices of the faithful tucked away in many of Rome's 900 churches.
In a cemetery under St. Maria della Concezione, a church looked after by the Italian Interior Ministry at the end of the famous Via Veneto, the Capuchin order of monks have arranged the bones of 4,000 of their deceased members into works of art. Originally buried beneath dirt from the Holy Land, the corpses were interred and rearranged in this way to make room for new arrivals.
Another little secret of the Capuchin Order: In the 19th century people believed they could pick winning lottery numbers. The mobs got so obsessed that Pope Gregory XVI had to banish one monk from Rome.
Miracles associated with Christian beliefs have been reported in places throughout the city.
There are 637 madonnas, or les madonelles, as they are called here. From the fourth century, they watched over passersby, protecting them on their journeys but also, they say, sometimes appeared in these representations. In 1796 there were 36 reported sightings of these madonnas moving their eyes.
The Virgin Mary is also said to have spoken to St. Gregory from a painting in a small chapel of the church named for him. And she appeared to Alphonse de Ratisbonne, a Jewish aristocrat who converted to Christianity on the spot in this church, St. Andrea delle Fratte, while he was waiting for his friend. There is a shrine marking the place.
On the ancient Appian Way, a church was built where Jesus convinced St. Peter not to flee Rome by appearing to him in a blinding light. Peter uttered the words Quo Vadis, Domine -- Where are you going, Lord? Quo Vadis is the name of the church.
But what about those secret spots that most tourists miss that have nothing to do with saints or gladiators?
There are a number of small museum gems, such as the Museum of Pasta, everything you ever wanted to know about Italians' favorite food.
Or the Museum of the Christmas Cribs, dedicated to nativity scenes, with more than 3,000 representations of where Jesus was born.
The Museum of Musical Instruments shows all kinds of ways to make music. Or, for the kid in you, there's the Museum of Playful Memory, dedicated to preserving childhood recollections.
The new discoveries continue each day. Just this month, while digging a new line for Rome's subway, an Imperial staircase was found. Previously unknown, archaeologists will have to unravel the latest secret find of the Eternal City.
With 26 centuries of history and mystery, there are many more secret spots, past and present, and the secret places at which to eat haven't even been mentioned.