The City Underneath: How San Clemente Holds Three Romes at Once

Rome grew upward, on top of itself. Over roughly two thousand years the ground level rose many metres, so temples ended up under houses, houses under churches, and the streets you walk are only the top floor of a much taller building. The Basilica di San Clemente, on Via Labicana below the Celian hill, is the single clearest place in the city to see that stack. Three cities sit one under the other at a single address, and once your eye learns to read them downward here, it reads the rest of Rome the same way.

One church, three floors of time

From the street, San Clemente looks like one handsome medieval church. Its floor is inlaid with swirling coloured stone, and a golden mosaic glows in the apse. That building went up in the early twelfth century, finished around eleven hundred and eight and completed by about eleven twenty-three. It was commissioned by Pope Paschal the Second, the same pope who had been elected in the church below, in the year ten ninety-nine. Call it the top floor.

Go down one level and the church you were standing in has an older twin beneath it, a basilica already documented by the year three hundred ninety-two and dedicated to Pope Clement the First, a figure from the very first century. Its walls carry early medieval frescoes, some of the oldest painted storytelling in the city. This lower church was buried, forgotten, and built over, its own roof becoming the new floor above.

Go down once more, to the first century, and you reach a Roman street with a private house, an industrial building, and a temple to the god Mithras. Its worship hall runs roughly nine and a half metres long. That level was rediscovered in eighteen sixty-seven, though standing water kept it from being fully explored until nineteen fourteen. The water is still there. A natural stream still moves through the deepest level, and if you stand quietly you can hear it running through the dark under the church.

The excavations were driven from the eighteen fifties onward by Joseph Mullooly, the Irish Dominican prior whose order has held San Clemente since sixteen sixty-seven. Three cities, one address, still stacked, and still holding everything above them up.

Why one stop opens the whole city

San Clemente is the opening beat of a walk that treats every arch, church, and stairway on and around the Celian hill as a layer resting on the one before it. Once you have descended those three floors, the lesson travels with you. The rest of the tour is Rome repeating the same trick at different scales, and knowing the pattern from San Clemente is what makes the later stops land. If you are mapping out how the neighbourhood fits together, the wider set of Rome walking tours puts this route in context.

The second stop plays the layering game more quietly. The Basilica dei Santi Giovanni e Paolo al Celio, founded in the year three hundred ninety-eight by a Roman senator named Pammachius, looks entirely finished from inside. Nothing in the nave hints at what lies below. Yet beneath the floor sit the Case Romane del Celio, about twenty decorated rooms belonging to at least five different buildings, layered together between the first and fourth centuries. They were rediscovered in eighteen eighty-seven by the basilica's own rector, Father Germano da San Stanislao. A courtyard room down there still holds a third-century painting of Proserpina drifting among small cherubs in a boat. You reach it from the ancient Clivo di Scauro, whose brick arches still stride across the lane overhead. (The John and Paul honoured here, worth noting, are fourth-century Roman martyrs, not the apostles from scripture.)

The Colosseum and an arch, read as layers

Come back down the hill and the Colosseum teaches the same lesson at a giant scale. Properly it is the Flavian Amphitheatre, named for the family that built it. Construction began under the emperor Vespasian around the year seventy-two, and it opened under his son Titus in the year eighty. It is the largest ancient amphitheatre ever built. Ancient writers claimed a capacity near eighty-seven thousand, though modern estimates settle nearer fifty thousand. Now read the ground it stands on. Before the stone oval existed, the emperor Nero had turned this valley into the private grounds of his Golden House, the Domus Aurea, with an artificial lake at its centre. The Flavian rulers drained the lake, filled the basin, and raised a place of public entertainment on top of it. A monument for everyone, on a drained lake, on the vanished dream of a single ruler.

A few steps away, the Arch of Constantine layers time inside one structure. Dedicated in the year three hundred fifteen by the Roman Senate to mark Constantine's victory over Maxentius at the Milvian Bridge, fought on the twenty-eighth of October in the year three hundred twelve, it rises about twenty-one metres high. Look closely and you are looking at several emperors at once. The arch was built with spolia, sculpture lifted from older monuments of the emperors Trajan, Hadrian, and Marcus Aurelius. By bolting himself to the images of Rome's admired predecessors, Constantine borrowed their authority in stone. Its inscription credits the win to instinctu divinitatis, inspired by the divine, a phrase worded to face both pagan and Christian readers at once.

Ending where Christian Rome began

One long, deliberate leg east carries the walk to San Giovanni in Laterano. This, not St Peter's, is the cathedral of Rome and the seat of the pope as Bishop of Rome. Founded in the year three hundred twenty-four under Pope Sylvester the First, on land tied to Constantine, it is the oldest of the four major papal basilicas and the only church in the world titled an archbasilica. Its inscription calls it the mother and head of all the churches of the city and the world. The baroque interior was reworked over a far older core, so the fourth-century foundation of papal Rome is still down inside this later skin, still functioning as the cathedral.

The walk closes across the piazza at the Scala Sancta, twenty-eight white marble steps that tradition, framed as legend rather than fact, links to Pontius Pilate's hall in Jerusalem and to Saint Helena, said to have brought them to Rome around the year three hundred twenty-six. Pope Sixtus the Fifth had them reinstalled in their present position in fifteen eighty-nine, and pilgrims still climb them on their knees. At the top sits the Sancta Sanctorum, the private chapel of the early popes and a surviving fragment of the medieval Lateran Palace. The palace was demolished and rebuilt, but this one room could not be erased, so the new building rose around it. The palace is gone. Its innermost room still stands on its old spot.

That is the whole argument in miniature: each new city rising on the one it could not quite throw away. Start at San Clemente, learn to look down, and the rest of Rome opens floor by floor.

Sources

• San Clemente, Rome (Wikipedia): the three-level basilica, the Mithraeum measured at about nine point six metres by six, the 1099 papal election below, and the Mullooly excavations.
• Basilica di San Clemente official history (basilicasanclemente.com): the Dominican custody granted in 1667 and Father Mullooly's excavation begun in 1857.
• Santi Giovanni e Paolo al Celio (Wikipedia): the 398 foundation by the senator Pammachius and the Case Romane del Celio rediscovered in 1887.
• Colosseum (Wikipedia): the Flavian Amphitheatre's construction, the 87,000 versus 50,000 capacity figures, and its siting over Nero's drained lake.
• Arch of Constantine (Wikipedia): the 315 dedication, the reused spolia from Trajan, Hadrian, and Marcus Aurelius, and the instinctu divinitatis inscription.