The drawing is based heavily on evidence in Vespignani’s sketchbook, fols. 7, 10, and 11 (Figures 3.8, 4.5, and 3.3, respectively in the book) as recounted in the main text. The rearrangement of the altar and the confessio within is based on differences recorded in the full dimensions of the frame supporting the Gregorian altar and its reworking under Gregory II, who enclosed it to the east with a vertical slab placed like a knife as reported with words and images in Vespignani's sketch.

The central entrance to the presbytery from the nave is speculative and contrary to the earliest evidence from Panvinio’s drawings from the 1560s (Figures 5.15 and 5.16); however, a more central entrance makes sense in light of processional liturgies and in light of the presence of a lower choir enclosure in the nave (not visible here).

The existence of a two-column ciborium over the altar of the Holy Innocent (at least by the sixteenth century) is certain, but its construction date and appearance are speculative. The pergola across the apse was plausibly built between ca. 700 and 815, but it remains of somewhat speculative appearance: it is unclear if the columns rose from a parapet or from the ground and the presence of gates is unclear and possibly redundant, given the presumed enclosures around the altars of Timothy and the Holy Innocents. The central entrance to the presbytery from the nave is speculative and contrary to the earliest evidence from Panvinio’s drawings from the 1560s (Figures 5.15 and 5.16); however, a more central entrance makes sense in light of processional liturgies and in light of the presence of a lower choir enclosure in the nave. The trabs maior is included at the springing of the triumphal arch and the inscription commemorating Leo III’s mandate is inscribed into the triumphal arch column in Figure 4.11.

Enclosed doors to the right and left of the crypt hall are the remainder of the hypothesized earlier access points to the crypt built by Gregory the Great. The shape of the altar is based on that present in the crypt at St. Peter’s. But between the thirteenth and late sixteenth centuries, we should imagine the furnishings to be those now transported to the Basilica of Nereo and Achilleo, for reasons specified in the book. The grate above the altar is documented by Vespignani’s sketchbook, fol. 15. Its position reflects the surveyed distance that the grate has from the reference point of the “PAULO” slab above (not seen, but flush with the presbytery floor that is broken to permit visibility above grade). Behind the grate is not the sarcophagus of Paul, but that of another “holy martyr of unknown name” (i.e. the “mysterious sarcophagus”), documented in both written sources and in Vespignani’s sketchbook fol. 12. The inclusion of niches (shaped like those in near contemporary crypts) for oil lamps is based on Gregory the Great’s provision of lamp oil to illuminate the space.

The transverse wall is well documented in views made just before the fire, its dimensions are derived from Alippi’s surveys. The presbytery’s position and appearance are based on Panvinio’s sketches and his description. The ciborium’s appearance is speculative.

The lower choir enclosure is positioned in the nave solely on the basis of the two pulpits reported by Panvinio in the 1560s. The size and appearance of the choir is hypothetical and based on the one present at San Clemente. The profile and size of a fragment of a cosmatesque barrier preserved in the Pauline cloister was used for the vertical trim detail around the entrance to the enclosure. The candelabrum was positioned in the vicinity of the southern pulpit, but not between the two pulpits as it is curiously depicted by Panvinio (Figure 4.9 in the book). By this point, the enclosure of the presbytery had been reworked by cosmatesque masters. Too little of its appearance is known to venture a reconstruction.

The new ciborium and frescos beneath the triumphal arch were commissioned by Abbot Bartholomew. The ciborium is only schematically modeled and the dimensions of the frescos are an estimate. Around this time, the monastic presence in the area of the presbytery was at its strongest and the entrance to the presbytery may have been shifted to the south (as documented in the 1560s by Panvinio) in order to provide direct access – over the marble intarsia floor (also of uncertain date) – to the monks entering the basilica from the cloister. Then again, this new asymmetric entrance may have come into play only at a later stage, when the popes were even less involved at St. Paul’s – for instance during the fourteenth century.

The existence of a canopy over the altar dedicated to Gregory the Great is certain, but its appearance is speculative and loosely based on documented medieval altars at St. Peter’s. The framework of piers and metal grate around the wooden statue of St. Paul is based on a combination of textual evidence and the detail from Maggi’s view of the statue – both from the early seventeenth century. Boniface IX’s statue is reported in its earliest known position with its original base. The fragmentary inscription above the frescos of the counter-façade is derived from Figure 3.15 in the book. The rose window is presumed to have been inserted on the occasion of the construction of the cavetto and façade mosaic (ca 1320s).

The appearance of the majority of the altars around the transept and nave at this time is unclear and thus they were assigned a generic mensa, predella, and gated enclosure. When a ciborium was reported, a generic ciborium was built in accordance with decisions made for Figure 5.32.

The operations undertaken by Sixtus V on the eastern flank of the presbytery and in the apse are based on written descriptions, which lack details that would offer this reconstruction more certitude. The biggest doubt concerns the entrance to the crypt beneath the presbytery once the eastern flank of that enclosure was removed. Also, were temporary barriers used to link the main altar with the apse, thereby creating a vast enclosed presbytery? A canopy over the throne in the apse is based on its existence in a period depiction on the ceiling of the Sistine Library (Figure 5.28 in the book).

The size of the confessio is based on Alippi’s plan. The appearance (from the rear) of the altar of the icon (and its counterpart to the south) is hypothetical given that it is only known in plan (Albertina AZ704, Figure 6.21 in the book). My reconstruction was inspired by Maderno’s altar currently in the Chapel of St. Lawrence, but resized in accordance with the Albertina plan. The alcove for St. Bridget’s statue is known from a number of post-fire views including Figure 5.11 and its precise dimensions were reported in Vespignani’s drawings (Figures A.6 and A.7 in the book). I have confirmed that Bridget’s statue would have fit inside the alcove without its current base.

For the architecture see annotations for Figure 6.9. The materials selected for the color rendering were derived from other known altar enclosures designed by Onofrio Longhi. Despite this, they remain speculative and incomplete. The statue of Bridget was turned to face the crucifix, a position that is tenable given that the statue's dimensions along that side would have fit within the shallow depth of the altar alcove.

For the architecture see annotations for Figure 6.9. The attentive viewer will note a mismatch in the capitals used for the altar of the crucifix, which could not be fixed before going to press.

The images in the oval and rectangular frames of the apse are based on known preparatory sketches for the paintings, or on photos made of the images that survived and are currently housed in the Pinacoteca of the monastery. The innermost image on the northern half of the apse is completely unknown and thus represented here in a faded hypothetical guise. Ornamental details of the frames were derived from Uggeri’s view from just after the 1823 fire (Figure 6.13 in the book). A few fragmentary, but highly sculpted portions of the apse – such as the angels flanking the main inscription or the putti faces above the side doors – were generated through photogrammetric modeling of extant fragments. The sculpted details were then grafted onto the three-dimensional model. Other sculpted details are merely Photoshoped into the image.

The main altarpiece “The Death of Benedict” by de Vecchi is known through an etching by J.J. Callot. The porphyry, central columns were spoliated from the presbytery of Leo III (Figures 4.9 and 4.11) and, thus, sized the same in each of these reconstructions. Their capitals were modeled with photogrammetry based on a nearly complete fragment currently in the entrance to the monastery’s modern courtyard. Other curious details such as the tapered pilasters are reported in Alippi’s surveys, Acquaroni’s view (Figure 5.11 in the book) and present also in other works by Onorio Longhi found in Rome (e.g. Palazzetto Altemps on the Capitoline Hill).

The position of these altars is described in period sources (see Chapter 6). They contain statues that were shifted with respect to when the altars were both in the southwestern arm of the transept. The altars are still extant, though slightly reworked, so I opted to base my reconstruction on images present in Tosi’s Raccolta (for example, Figure 6.5 in the book). The images within the brass door panels are not necessarily in their original order, though they are based on Alippi’s image published in 1815.