Envisioning Old St. Peter's: The Interior from the Time of Constantine through the Renaissance

In a previous article we considered what the exterior of Old St. Peter's was like and today we will turn our attention to the interior of the same.  In many regards, to envision the interior of the old Constantinian basilica, just as with the exterior, we should first bring to mind San Paolo fuori le Mura and we can begin to image the experience of walking into St. Peter's.

I. General Layout

Old St. Peter's was a classic Roman basilica from all accounts, and like any basilica that had survived for over a millennium, we have to bear in mind that there were changes to the interior decoration and arrangement as the centuries slipped past. In that regard, our considerations of what "Old St. Peter's" was like has to be a layered considerations of its history, just as does history generally in its own right.


The general layout of the interior basilica was classically 'Roman' and one need only bring to mind the basilica of St. Paul's to picture it. The following diagram shows the layout of old St. Peter's as it stood in the middle ageas:


Anyone who has visited San Paolo will immediately recognize the similarities with the double row of columns lining the nave leading up toward the high altar. While not all of these features shown here were to be found in the Constantinian era, the bones of the basilica are indeed Constantinian in its basic basilica form. 

II. Altar and Sanctuary - Evolution from Constantine to Gregory the Great

As for the altar and sanctuary, its form in particular was not static over the centuries, but in general what we have to imagine, if we wish to imagine what was prior to its demolition in the Renaissance, is the main altar higher than the level of the nave with a confessio like structure beneath as it is in many Roman churches. Below (left) we can see an illustration of this arrangement as depicted in 1580; on the right we can see a contemporary reconstruction that sets it better into its broader context (thought with a few caveats we will discuss below). This was not the original Constantinian form of the altar and sanctuary let it be noted, but it was the arrangement that characterized Old St. Peter's for most of its existence.


Not shown in either illustration is the balustrade that sat before the altar. That is shown better here in this digital reconstruction of the later form of Old St. Peter's produced by Cambridge University.


However, as mentioned before, prior even to this arrangement there was yet an earlier one; the Constantinian one. Already by the year 440 we see this depicted on the Samagher casket -- a casket of ivory that was discovered in the early 20th century beneath the altar of a church in what is today Samagher, Croatia. On the one side of the casket, thought to have possibly been a gift from the pope to the Emperor Valentian III, we see a depiction of the ancient presbytery of Old St. Peter's and the "memoria Petri" that was erected by Constantine around and over the original tomb of the apostle. While part of the ivory has regrettably fallen off, one can still see serpentine columns on both the ciborium like structure as well as a balustrade.The figures of Constantine and Helena are thought to be depicted as part of the representation as well. 

Another, more contemporary reconstruction of the same memoria of the apostle can be seen here in these illustrations, representing the original Constantinian arrangement:

To be clear, what is shown here is not an altar.. Those who would like a more detailed explanation of the underlying archeology of this may also wish to revisit our article on What Sits Underneath St. Peter's Basilica, but suffice it to simply summarize it this way: the Constantinian basilica was build overtop a Roman cemetery in which Peter's tomb was found and, in time, overtop the tomb of St. Peter itself there was a structure built over it. (See below). 

Constantine would alter this cemetery structure and build his memoria around it, made from marble and  strips of red porphyry (the back of which can still be seen from the Clementine chapel found beneath the high altar of St. Peter's today:

Left: The excavations beneath the present high altar of the basilica showing the backside of Constantine's memoria, the red porphyry strips being clearly visible as well as the lighter colour marble. Right: The same location seen today as part of the Clementine chapel.  What you are looking at behind the golden grille is the back of Constantine's memoria that he built around and over St. Peter's tomb.

Over-top this memoria structure was then added the ciborium like structure with a corona lucis hanging from the middle of it. Around it all was a short balustrade and it would seem that the actual altar itself would have come to sit within the balustrades and before the memoria.  (This approach of building what amounts to a kind of building within a building may seem strange to us today, but I'd invite you to consider the Church of the Holy Sepulchre in Jerusalem which likewise has a separate building like structure built right in the heart of the church to enclose the sacred spot around which the larger building was erected.)

To bring this all together as regards old St. Peter's and how this evolved from Constantine's time to the time of Gregory the Great, this arrangement would come to be modified in such a way that Constantine's memoria would see the floor around it raised on all sides but the front with the altar being built directly overtop the memoria. Essentially it would now take the form of a confessio

The following illustrations will help in understanding what developed and how.

Left: The original Constantinian memoria with a small balustrade and ciborium like structure built around and over it. Right: The sixth to seventh century arrangement showing the level of the altar and sanctuary now raised with the new altar and ciborium built directly over the original Constantinian memoria. The surrounding structure or the original arrangement was necessarily removed

Top: Model showing the original Constantinian memoria with its short balustrade just visible behind and two of the four serpentine columns. Bottom: The sixth to seventh century arrangement showing the altar and ciborium built over the Constantinian memoria.

The yellow coloured marble above the memoria, shown in the model above, is the seventh century altar which can now be seen sitting over top the entrance to Constantine's memoria which has been built around on three sides creating a new floor level within the apse. Steps on either side up lead up into the apse and behind would have been the semi-circular synthronon with the throne in the middle.  

The following schema may help to provide further contextual insights into the arrangement as it developed from the time of Peter's original tomb and cemetery shrine, to the Constantinian memoria (which was built from and around the same cemetery shrine) and finally to the arrangement from the sixth to seventh century until the Renaissance which was built over it.


The net result as this developed then would have started out a little bit like the Holy Sepulchre in Jerusalem, with the sepulchral monument -at the very heart of the basilica, then moving toward something more akin to Santa Cecilia in Trastevere (as well as some other Roman basilicas) where we see the altar and sanctuary raised up from the floor level of the nave, steps leading up to it on either side, with the high altar sitting over top the tomb / relics. As in Santa Maria in Cosmedin, a balustrade then sat before that. 

III. Mosaics of the Apse and Triumphal Arch

As we begin to move away from the altar, two of the more prominent features of any Roman basilica are invariably the apsidal mosaic and the mosaics of the triumphal arch. 

Visible here in this reconstruction is the mosaic above the triumphal arch which depicted the Emperor Constantine offering Christ a model of the basilica.


For the apse, we see here a mosaic that depicted Ss. Peter and Paul to either side of Christ enthroned. Two palm trees -- symbols of martyrdom and victory over death -- are also depicted.  Beneath this on the lower register we see 12 lambs representing the apostles

The only pieces of this apse mosaic that are known to survive down to our own time are two tiny fragments, now located in the Museo di Roma (Palazzo Braschi) just off Piazza Navona. These remnants depict a phoenix -- a resurrection symbol -- and Pope Innocent III.  To the right they are placed within their original apsidal context (thereby also showing us how truly little we have left). Here again, if we want to imagine what it might have looked like in reality, certainly there are some similarities in this design to that found in the basilica of San Paolo as well. 

One of the elements that one might note above is the suspended, candlelit cross hanging above balustrade. 

V. The Choir and Ambo

Flowing from the sixth to seventh century adaptations of the Constantinian memoria we also see the addition of a schola cantorum along with the two ambo on either side -- one for the epistle and one for the gospel -- very much akin to what one would find today in the basilica of San Clemente. There too was a permanent paschal candlestick stand just as in San Clemente. 

A view looking down from the high altar into the schola cantorum toward the narthex.

A view from the nave toward the schola cantorum and high altar. The two ambos can be seen to either side.

Taking San Clemente in mind then and putting this on a more grandiose scale, one can readily imagine this arrangement with the altar and its ciborium looming high above, just as it does in San Clemente, the schola cantorum reaching out like great arms drawing one toward the altar and tomb of St. Peter.  


We can expect that this was decorated in the fashion that we similarly see in other churches in Rome that still retain this feature.

V. The Nave and Transepts

As we proceed into the nave we have to distinguish once again between the very most ancient form of the basilica and then the basilica as other liturgical elements were added -- monuments, additional altars and so on. One can simply assume as in any such instance that, as the centuries pass, there would be more and more accumulation of such objects within the basilica -- and that is certainly the case with old St. Peter's as well.

As was shown earlier, old St. Peter's, like present day St. Paul's, had a double row of columns to either side supporting the massive structure. Of particular interest to us are the main interior columns located within the central nave.  These columns were made up of various colours and types of stone -- a sight one can still see today in various Roman basilicas whose columns frequently came from other ancient buildings as spoila -- just as in the case of old St. Peter's.


An artistic representation of what the interior might have appeared like from the nave prior to the seventh century.

A digital reconstruction of what the nave might have appeared like from the nave after the seventh century until the end of its existence. The structure located to the right, within the nave, was the canons' chapel/choir (a further image of this below). 

The canons' choir.

The columns of old St. Peter's were made up of various types and colours of stone as mentioned. We know which types of stone and they can be seen depicted here.

This might seem odd to us today, for we are rather more accustomed to everything matching, but this variance of form and colour must have been quite striking, adding an additional decorative element, but in a time when we are dealing with the use of spoila, this mismatching is to be expected for simple reasons of practicality and what was available (and frankly is part of the charm of these buildings). 

During the Constantinian period up until the eleventh century the pavement (i.e. floor) of the basilica was made of white marble, possibly ornamented with some red porphyry bordering within the nave proper. By the twelfth century this was replaced with usual sort of cosmati:

A view of the pavement of St. Peter's as it might have looked from the 12th century onward

As we look up within the nave toward the clerestory levels we would have been greeted with further marble work, and by a certain point, possibly as early as the fifth century, these began to be decorated with further imagery. 

A reconstruction of the nave as it might have appeared in the fourth century (left half) and fifth (right).

The depiction on the walls of the nave were made up of frescoes and/or mosaics which depicted scenes from both the Old and New Testaments in a kind of chronological order of salvation history, as well figures of the apostles, angels, saints and popes.



A view from the behind the oratory of Sixtus II looking toward the nave

Going down along the outer edges of the building would have been -- much like we are accustomed to seeing in these great basilicas today -- various tombs, side altars and chapels that would have multiplied as the centuries passed. 

Fragment of an early eighth century mosaic of the Adoration of the Magi, formerly found in chapel of the Blessed Virgin in Old St. Peter's -- now located in the sacristy of S. Maria in Cosmedin

It is worth noting here is that what one is not really getting a sense of here is the basilica in its fully furnished, liturgical form -- that is to say, with all its liturgical ornaments in place (which were frequently sacked sorry to say). The Liber Pontificalis -- which cannot always be taken verbatim -- tries to recount some of these elements such as ten foot high standards (candelabra magna) of silver that were said to be ornamented with scenes of the apostles, as well as silver oil lamps (perhaps in the form of coronae) that included the forms of dolphins, and a coffered gold ceiling above the memoria of Constantine -- while the rest of the ceiling was open timber beams apparently.  We read also of bejewelled, metallic coverings for the altar and of a great lit iron cross and keys that hung over the tomb of St. Peter before the altar.

We also read of olfactory qualities that one might have experienced upon entering the basilica, like the use of spikenard oil in the lamps which would have given off a musty and woodsy scent, as well as the use of fragrant beeswas and pine torches.  

From a lighting perspective, the oil lamps and standing candles have already been mentioned, and it is said that 150 lamps were lit everyday within the basilica. 

Certainly the overall picture and atmosphere we are gaining here, as things even stood already by the initial centuries of its existence, is of a well furnished basilica gleaming with the flicker of flame that reflected off the bejewelled gold and silver ornaments, surrounded by polychrome marbles taken from all corners of the Roman empire, hinted with the scents of pine, beeswax and nard.  It must have been striking to all the senses -- especially when the sacred liturgy of the ancient and venerable Roman rite was taking place within.

Of course it is worth noting that many of the specific elements here in these reconstructions are theorized and should not be taken too literally, but perhaps this will give readers some sense of what the old Constantinian basilica must have been like. 

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