Basilica di San Clemente

The multilayered church representing two millennia of Roman history

Christians worshiping in Rome under the Pagan emperors did so at domus ecclesiae – ‘church houses’. There, in private property, and in blunt refutation of the public religious ceremonies of antiquity, they gathered to practice their ‘most mischievous superstition’ (Tacitus). The archaeological record so far furnishes no evidence of these domus ecclesiae within the city walls. What it does provide are tituli, ‘legal titles’, in essence the earliest formal, structured parish churches, each with a cardinal, established after the Edict of Milan in 313 which allowed Christians to worship openly within the Roman Empire.

Just down the road from the Colosseum, on the street leading to San Giovanni in Laterano, Rome’s cathedral, sits one of the earliest tituli, the Basilica di San Clemente. The modest exterior of this rather battered looking church belies one of Rome’s most dramatic interiors, with three layers of buildings piled on top of one another, each one a time capsule of Roman history. The church seen from the street is a twelfth-century basilica; beneath it rests a fourth-century predecessor; and further underground still, even older buildings from the first century onwards, including a Mithraic temple. Together, these structures testify to 2000 years of habitation and worship in brick and concrete.

In 1857, Father Joseph Mullooly began excavating beneath San Clemente, discovering not only the fourth-century church below, but first century dwellings further down. [Image: Wikimedia Commons]

The current basilica, with a smallish nave, narrow aisles and apse, is a patchwork of the accumulated decoration of eight centuries. Its exterior is modest, even unremarkable, with a relatively subdued and understated Baroque façade by Carlo Stefano Fontana (nephew of the better-known Carlo Fontana). The atrium is the best-preserved of any to survive from medieval Rome, with columns of grey and red granite topped mainly by Ionic capitals, both from antiquity and the 1100s. Inside, and in typical Roman fashion, the nave pavement is Cosmatesque, with the swirling guilloche leading directly to the schola cantorum (the choir), made from Proconnesian marble. The church is almost exactly in-line with the former church below, with the columns on the left standing directly on top of the subterranean columns underfoot.

The highlight of the current church is its apse, a lavishly decorated mosaic of the crucified Christ. The mosaic is extended to the triumphal arch framing the apse, with depictions of Christ Pantocrator and the symbols of the evangelists. The mosaic, one of the best in the city, testifies to the large artistic shadow cast by the Byzantine Empire (far wealthier than Rome at the time, and undergoing a political and artistic renaissance), and the superb craftsmanship of those who assembled it. The style is early Christian (see the fifth-century mosaic cycle at Santa Maria Maggiore, where a vine motif is also in evidence); whether the design is a direct copy of the apse mosaic that existed in the former San Clemente below is unknown. In any case, it is pointedly executed in a manner that evokes Late Antiquity, not only advertising San Clemente’s ancient history but expressing continuity with the older church over which the new basilica was erected.

The decision to build today’s twelfth-century church was made after the original fourth-century building fell into a dilapidated state. Mounds of earth and rubble were simply filled into the old church, and the current building was constructed on top. The older church thus disappeared for almost 700 years, until Father Joseph Mullooly (Irish Dominicans have inhabited San Clemente since 1667) began tunneling in 1857. It is to Mullooly and his Stakhanovite work-ethic beneath San Clemente to whom we owe our gratitude for our casual wanderings under the church today. During the 1860s, Mullooly of his own initiative removed the debris from the fourth-century church on this second level, and partly excavated the older structures beneath it – 130,000 cartloads of earth in eight years. For a century his example encouraged others to perform similar feats, selfless acts from curious minds for which we should give thanks.

The second, middle layer of San Clemente cleared by Mullooly is a basilica built at some point in the fourth century. The date of its construction is not known, and is complicated by the fact that early tituli with names corresponding to existing churches may not have been the same place; in other words, a titulis Clementis existed in Rome around 200 AD, but it doesn’t mean it was this building. A church in Rome dedicated to St Clement is referred to by Jerome in his biography of early Church fathers De Viris Illustribus (On Illustrious Men) of 392. This was long thought to refer to San Clemente, but this has been challenged by scholars since Mullooly’s excavations. Bluntly, nobody knows when the church beneath San Clemente was constructed; some time in the late fourth century seems likely.

Certainly, it was up and running by 417 when Pope Zosimus held a council there. Scattered throughout the old church, which is laid out in the basilica style, are deteriorating frescoes of varied artistic quality, as well as columns, epitaphs, floor mosaics and a pagan sarcophagus. The well-tended tomb of St Cyril is also on this level. Cyril, along with his brother Methodius, was the evangelist of the Slavic people. Credited as the father of Glagolitic alphabet, the earliest Slavic script, Cyril also initiated the first Slavic civil code and in the ninth century, with his brother brought back to Rome and to San Clemente what they believed were the relics of St Clement himself, who was apocryphally thought to have been martyred in the Crimea.

The fourth-century church is understandably fragmentary. Modern buttresses supporting the church above, as well as the reduced height of the ceiling, impede attempts to try and see the church as it would have looked in, say, the seventh century. But it is churlish to complain given the effort that went into clearing this space, and in any case, it is with immense pleasure that one can get up close to once buried artworks previously consigned to oblivion. The subterranean setting, and the slowly peeling frescoes, paradoxically make this the level where the antiquity of the site comes into sharpest focus.

Harrowing of Hell depiction in fresco in the lower basilica at San Clemente. [Image: Wikimedia Commons, Ulrich Mayring]

Below the fourth-century level, and deep beneath today’s basilica, are the oldest structures at San Clemente, dating to the first century. Excavations in the 1800s revealed a series of buildings including a Mithraeum, a temple to that obscure, Christ-like god Mithras. Neither a deity from the Greco-Roman canon nor derived from the Abrahamic faiths, Mirthraism is Persian in origin, from the Zoroastrian god Mithra. It was adapted by the Greeks and spread across the Roman Empire, with Mithraea found in such diffuse places like Britain, Syria, Germany and Bosnia. More than half a dozen Mithraea have been discovered in Rome itself, and the variety of extant temples suggests that the cult of Mithras was widely adopted. But it did not in fact challenge the existing Roman status-quo. However, it is thought to have been a rival to that other new faith also then seeking worshipers, Christianity.

Mithraism shared many features with Christianity. Mithras delivered salvation to mankind, those who worshiped him were promised life after death if they made the correct propitiation, and there was a strong emphasis on morality. Yet the comparisons only go so far. Strictly male-only, most of Mirthraism’s devotees were soldiers (who campaigning abroad, had brought the cult back to Rome), to whom its rigid code of obedience was attractive. By the fourth century Mithraism was in terminable decline, crushed under the new official state religion of Christianity and its swelling number of adherents. Its fate was sealed, like all cults, during the rule of Theodosius I in the 390s, but its defeat can actually be put down to what attracted people to it in the first place: Mithraism’s self-limiting approach of excluding women, as well as its secretive and esoteric nature, withered when compared against the all-inclusive Christian faith, which welcomed all and revealed everything you needed to know from the outset.

The Mithreaum at San Clemente’s bottom level. The relief on the altar depicts Mithras slaying a bull, part of Mithraism’s creation myth. [Image: Wikimedia Commons,

The Mithraeum at San Clemente was built into the existing second-century structure – thought to be a nobleman’s house – in the third century. Building a church over the Mirthraeum was likely deliberate, a means by which Christians could either ‘assume the significance, power and sanctity of the place – or obliterate its dangerous pagan associations’.[1] Other Mithraea have been discovered beneath ancient churches in Rome, but at San Clemente it is probable that this one continued to be used even as the church above it was in use (the fourth century church does not sit directly over the Mithraeum) before eventually being filled in.

It is at this lowest level that history recedes and conjecture emerges. The large building near the Mithraeum, exactly 100 Roman feet wide, is thought by some to have been an imperial mint, but no hard evidence backs up this claim. It is possible that buildings at this level were damaged in the fire that devastated Rome in 64. In any case, when excavations were undertaken in 1912 it was found that there was an underground lake submerging most of the structures. Undaunted by this, one Father Nolan ‘courageously tackled the problem, boring a tunnel of some 700 yards from the Cloaca Maxima at the Colosseum back to San Clemente at a depth of some forty feet under Via Labicana’.[2] A small spring of fresh water still flows down there.

Room at the lowest level of San Clemente, from the first century. [Image: Wikimedia Commons, Valerio b. cosentino]

Making sense of San Clemente is not easy. A broad delineation between different historical periods is clear enough in the three layers of construction. But a more comprehensive understanding eludes us, and always will. The site will therefore forever remain alluring, never fully revealing its secrets. In the meantime, we can look at San Clemente as a metaphor for Rome itself: swept up in flames, repurposed, buried, built over, incorporated, buried again and, like the phoenix in the current church’s apse, capable always of resurrection and renewal.  


[1] Maria Fabricius Hansen 2015: 114.

[2] Leonard Boyle 1960: 71


Boyle, L. 1960. St Clement’s: Rome. Rome.

Churches of Rome Wiki, ‘San Clemente’: – accessed September 2020

Hansen, M, F (trans. Haveland, B, J). 2015. The Spolia Churches of Rome. Denmark.

Taylor, R, Rinne, K, W, and Kostof, S. 2016. Rome: An Urban History from Antiquity to the Present. Cambridge.

Jake Plenderleith

Writer and editor, passionate about Rome.

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