The Basilica of San Clemente is situated some three hundred yards above the Colosseum, on a road that rises gradually to St John Lateran from the valley between the Coelian Hill on the south and the Oppian Hill on the north.

It is named after Pope St Clement, the third successor of St Peter in the See of Rome, who died about 100 A.D. Until a hundred years ago, indeed, it was commonly thought that the present church was that to which St Jerome re¬ferred when he wrote about 390 that « a church in Rome preserves the memory of St Cle¬ment to this day ».

But in 1857, Fr Joseph Mullooly, the then Prior of San Clemente, began excavations under the present basilica, uncovering in the process not only the original, fourth- century basilica directly underneath, but also at a still lower level, the remains of an earlier, first-century building. Later excavations, notably those conducted in 1912-1914 by Fr Louis Nolan when a drain was being built between San Clemente and the Colosseum, show¬ed that underneath this third layer of buildings there was still a fourth stratum, that contain¬ing buildings destroyed in the fire of Nero in 64 A.D.

The level, therefore, of the valley in which San Clemente lies was about sixty feet lower in the first century than the present level.
After the fire of 64 the gutted buildings were filled in and used as foundations for further houses, at a level that is roughly that of the floor of the Colosseum today.

At this third level at San Clemente there are two buildings that are separated from each other by a narrow passage¬way. The less pretentious of these is a brick building, possibly an « insula » or apartment house, in the courtyard of which there is a small Mithraic temple of the end of the second century.

Across the passageway there is a more magnificent, rectangular structure built of lar¬ge tufa blocks that support walls of brick mounted on travertine or porous, light-yellow rock.
Within this rectangle there is a great, open space or courtyard that is considerably larger than the nave of the present basilica. A rectangular building, the first church at San Clemente oc¬cupies exactly the area of the first-century, « Clementine » palazzo.

The fourth-century archi¬tects simply filled in the ground-floor rooms and the courtyard to the level of the first storey.
The courtyard of this new level became the nave of the church, the rooms that once overlooked the old courtyard on either side being converted into the south (Via S. Giovanni) and north aisles as we see them today.

Meanwhile, side by side with this church but now at a lower level, there still continued to exist the Mithraic religion in the adjacent brick apartment-house. In 395, how¬ever, Mithraism was outlawed, and sometime afterwards the area was acquired by the clergy of San Clemente, who then proceeded to add an apse to their rectangular church, projecting it out over the vestibule of the Mithraic temple and filling in the remainder of the area.

The completed basilica survived until about 1100, when it was found that the building was unsafe and should be abandoned, possibly because of destruction caused in the neighbourhood by the Normans under Robert Guiscard when coming to the rescue of Pope Gregory VII in 1084.

At the instigation of the then Cardinal Titular of San Clemente, Anastasius (ca 1099 - ca 1125), the fourth- century church was now filled in with rubble to the top of the pillars that set off the nave from the aisles, and on these foundations a replica of the old basilica was erected, but on a slightly smaller scale.

And thus a new San Clemente, the present one, appeared at a still higher level above the old floor of the valley; and the original basilica and the level on which it rest¬ed were so effectively abandoned that they were utterly forgotten in time until some seven hundred years later, when the great excavations under Fr Mullooly and « the father of ar¬chaeology ».

De Rossi, brought them to light between 1857 and 1870. It is generally assumed in books on San Clemente that a Benedictine community occupied the original basilica from the sixth century onwards, but is clearly due to a misreading of a passage in the Dialogues of Pope Gregory the Great (590-604).

In fact it was only in 1403 that a monastic community began to serve San Clemente, when Pope Boniface IX introduced the newly-founded Augusti- nian Congregation of St Ambrose (1379) from Milan. The basilica remained in Ambrosian hands until 1643, when Urban VIII suppressed the whole Congregation.

In 1645 the Domi¬nicans of San Sisto were put in as caretakers by Camillo Pamphilj, the Cardinal-nephew of In¬nocent X, the whole property being handed over in perpetuity to the Dominican Order in 1667 by Cardinal Francis Maidalchini, Pamphilj’s successor as Commendatory abbot of San Clemen¬te.

Ten years later, because of religious persecution in Ireland, the basilica and convent of San Clemente, together with those of San Sisto Vecchio opposite the Baths of Caracalla, were granted to the Irish Dominicans.