Once upon a time there was a natural spring bubbling up at this spot in what was then the grassy outskirts of early Rome. It is reasonable to guess that a modest cult site might have sprung up around this spring, honoring its nymph or some such, as was quite common. In time, the city expanded and this once-abandoned area became desirable for industrial use as the Republic gained an empire. The Republic’s Mint was built here, making use of the convenient ice cold water, and likely continuing to honor its associated spirit. Decades pass, a century, two, Rome expands still further, and chaos raises an Emperor. After the Great Fire of 64 AD, it becomes convenient to move the Mint out of what is now a desirable central district of the expanding city, so the site is purchased by a wealthy Roman who builds his house here. Decades pass and the builder, or his son, is converted to the exciting cult of this new god Mithras who promises his followers, not the gray mists of Hades, but resurrection and eternity. Since he is wealthy, he converts his home to the use of the cult, and digs tunnels and creates the underground Mithraeum. For a generation or two this villa hosts the cult, but then Constantine comes to power and a new cult promising an even more inclusive form of salvation comes into vogue. The villa, which is now three hundred years old, is buried, a convenient architectural choice since the ground level of the city has risen several times due to regular Tiber floods, so the old house was in a low spot. A new church is built on top, and serves the Roman Christians of the local community for a few generations. The fall of Rome is usually marked at the first sack by they Visigoths in 410 or the sack by the Vandals in 455, but the conquerors are also Christian so the church stands and still serves the neighborhood, though its population is much smaller. Now the main Emperor moves to the East, and in the 500s, when the church is about 200 years old, someone paints a portrait of the empress on the wall, then a generation later someone else decides a Madonna is more appropriate, and puts a baby in her lap. Two or three more generations go by and Cyril and Methodius bring the bones of Clement from the East, and they are buried here, a great day for the neighborhood! Commemorated with more frescoes.
Another century, two, we are well into the Middle Ages, and this old Roman building is old-fashioned and very low since the ground level has risen further. The local community, and devotees of St. Clement, decide to build a new church. They loot columns and flooring from other Roman sites, and bury the old church, producing the 12th century structure above, but using the walls of the older one as the foundation, so the arches still show in the walls. The new church is very plain, but is soon decorated using mosaics provided by Eastern artists who come to visit Clement and Cyril. After a few generations the Renaissance begins, and we call in a fashionable Florentine-style artist to fresco one chapel. A few centuries later Pope Clement VIII comes to power and decides to spiff up San Clemente, initiating the internal redecoration which will end with the ornate baroque ceiling.
Oh, and somewhere in there someone slapped on a courtyard on the outside in a Neoclassical style, because it became vogue for buildings to look classical, so we may as well add a faux-classical facade onto this medieval building which we no longer remember has a real classical building hidden underneath. Not long after the Baroque redecoration is begun, the nineteenth-century interest in archaeology notices those arches in the walls, and starts digging, re-exposing the lower layers. Devotees of St. Cyril and lovers of history, like the head of the Vatican Library, begin to flock to San Clemente as an example of Rome’s long and layered history, and so it gains more layers in the 20th century as donations and burials are added to it. Every century from the Republican Roman construction of the Mint to the 20th century tombs is physically present, actually physically represented by an artifact which is still part of this building which has been being built and rebuilt for over 2,000 years. Not a single century passed in which this spot was not being used and transformed, and every transformation is still here. And all that time, from the first sacred spring, to the Mithraism, to today’s Irish Dominicans, this spot has been sacred.
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This is Rome.
San Clemente is exceptional in that it has been largely excavated and is accessible, but every single building in Rome is like this, built on medieval foundations which are built on classical ones. I can’t tell you how many times I’ve gone into a random pizzeria and found a Renaissance fresco, or a medieval beam, or Roman marble. I’ve gone into a cafe restroom and discovered the back wall was curved because this was built on the foundations of Pompey’s theater (where Caesar was assassinated). I’ve gone into churches to discover their restrooms used to be part of different churches. Friends have this experience too. During my Fulbright year in Italy I had a colleague who was studying Roman altars, half of which you could only get at by ringing the bell of strangers’ apartments and saying: “Hello! I’m an archaeologist, and according to this list there’s a Roman sacrificial altar here?” to which the standard response is, “Oh, yes, come on in, it’s in the basement next to the washing machine.” I have another friend who thinks he’s found a lost chapel frescoed by a major Renaissance artist hidden in an elevator shaft. Another friend once told me of a pizza place with a trap door down to not-yet-tallied catacombs. I believe it.