A year later, Casali submitted to the same publisher the considerably more extensive treatise on Christian rites “De veteribus Christianorum ritibus”, which had already been announced in the preface “Ad Lectorem” in 1644 (Fig. 3, ThesaurusID 23881295). [4]

In order to distribute the volumes, which were unaltered from the Roman edition, in France via the Parisian bookseller Siméon Piget (active 1639–1668), all three treatises were published together in 1646 under the new collective title “Sacrae prophanaeque religionis vetustiora monumenta” and with a new additional title page (Fig. 4). [5]

As his previously published “fragment of early Christian rites [... contained] numerous errors regarding authorship and printing” [6] Casali had an expanded version of the Christian rites published in Rome just one year later, in 1647, this time by Bernardino Tani (active 1637–1649) (Fig. 5, ThesaurusID 23881420).

The revisions and additions concern both the text and the illustrations: four new woodcut illustrations depicting further cross forms have been added (ThesaurusID 23881457, ThesaurusID 23881458, ThesaurusID 23881459, ThesaurusID 23881460) as well as a copper engraving depicting the so-called rain miracle on the Column of Marcus Aurelius (ThesaurusID 23881448).

Finally, following Casali’s death (1648), this revised treatise on Christian rites was published once again as a three-part work under the title “De profanis et sacris veteribus ritibus opus tripartitum”, together with “De veteribus AEgyptiorum ritibus” and “De antiquis Romanorum ritibus”, by Thomas Heinrich Hauenstein in Frankfurt and Hanover in 1681 (Fig. 6, ThesaurusID 1369099). For this, Hauenstein had all the illustrations re-engraved on copper plates.

As with “De profanis et sacris veteribus ritibus”, Casali largely draws on artefacts from his own collection to illustrate Christian rites. [7] These include an enkolpion (ThesaurusID 23983040), a pilgrim’s badge (ThesaurusID 24007200) and a pendant (ThesaurusID 24007204) each in the shape of a cross. Most of the remaining depictions of crosses are derived from Giacomo Bosio’s (1544–1627) [8] historical-theological reflection on the cross and its symbols, “La trionfante e gloriosa croce” (ThesaurusID 1737418), which had been published 35 and 37 years earlier respectively. However, in most cases Casali does not explicitly cite Bosio as the source. [9] For instance, in 1647 Casali adopts Bosio’s illustration of two lambs with a cross and a Christogram without naming him. Even though the woodcutter working for Casali eliminates the surrounding landscape in his depiction, the copied original remains recognisable (Fig. 7 and Fig. 8, ThesaurusID 23875122, ThesaurusID 23881459).

The text accompanying the illustration states that the lambs are depicted in ancient marble monuments. [10] However, in both Casali’s and Bosio’s works, the illustration serves to illustrate lambs crowned with a cross or Christogram as a visual element of Christian monuments, rather than to depict a specific artefact: Bosio states that such lambs crowned with a cross or Christogram can be seen on Christian sarcophagi found in Rome. [11] Although the major 17th-century work on Christian archaeology, “Roma Sotterranea”, by his nephew Antonio Bosio (1576–1629), was only published posthumously in 1632/34, [12] it can nevertheless be considered a reference for Bosio. For work on it had already been ongoing for several decades since the end of the 16th century: by 1615, some of the plates for the planned work were reportedly already printed. [13] Even Giacomo Bosio himself refers to his nephew’s work and book as early as 1610: “E di essi fà particolar mentione Antonio Bosio mio Nepote, nel suo Libro deʼ Sacri Cemiterij, intitolato Roma Subterranea.” [14]

Antonio Bosio’s publication contains only three sarcophagi featuring such lambs: one with a Christogram and two with a simple cross. All three sarcophagi have survived, are still located in Rome, and have been included in the repertory of early Christian sarcophagi [15]: The columnar sarcophagus, which depicts a lamb with a Christogram alongside Christ on its front, is now in the Basilica of San Pietro in Vaticano (Fig. 9), [16] whilst the columnar sarcophagus featuring the agnus dei crowned by a cross is now kept in the Papal Basilica of San Paolo fuori le mura (Fig. 10). [17]

The front of the second sarcophagus, featuring a lamb surmounted by a cross, is in turn part of the collection of the Museo Pio Cristiano of the Musei Vaticani, albeit in a fragmented state (Fig. 11). [18]

In all three cases, the lambs face the viewer much more directly than in the woodcut in “La trionfante e gloriosa croce”. This suggests that, despite referring to the sarcophagi featured in both “Roma Sotteranea” in 1610 and the “Repertorium”, Giacomo Bosio did not simply mimic the depiction of the lambs on the sarcophagi.

When discussing crosses in early Christian mosaics in 1645, Casali also draws on visual material previously published by Bosio. This is the case, for instance, with the detail featuring a gemstone cross and a lamb from the apse mosaic of Old St Peter’s (Fig. 12 and Fig. 13), which by that time had already been lost for 53 years in the course of the construction of the new basilica. [19]

In his work, Bosio states that he is in possession of a copy of a drawing of the tribuna of Old St Peter’s, which was commissioned by the canons of St Peter’s prior to the destruction of the apse and whose fidelity to the original was certified by a notary. [20] He can only be referring to the watercolour pen-and-ink drawing now found in the so-called Grimaldi Album. [21] The parchment contains, beneath the drawing of the mosaic, a description and a certification by the Capitoline notary Quintiliano Gargario dated 3 August 1592.

In her 2004 essay, Antonella Ballardini traces the genesis of this drawing and its subsequent circulation in manuscripts, and classifies all known copies into a stemma based on their relationships.[22] According to this, there are only three copies that were produced before 1610, the year Bosio’s book was published, and which could therefore be considered as Bosio’s source. [23] Two are found in an album belonging to Alfonso Chacón (1540–1599) [24] and, like the third copy [25] – which, according to Ballardini, is also linked to Chacón – can therefore be dated to before his death in 1599. This third copy, now in the possession of the Biblioteca Angelica, is a collage. In the drawing on fol. 31v–32r in Vat. lat. 5408 from Chacón’s collection, Ballardini sees a copy of that collage by the same artist. Whilst the highly simplified depiction of the lamb rules out the Angelica collage and its copy as a model for Bosio, the similarities between the drawing authenticated by Gargario in the Grimaldi Album and its copy on fol. 29v–30r in Vat. lat. 5408 from Chacón’s collection make it difficult to reach a definitive conclusion (Fig. 14). One striking difference remains the streams of blood flowing from the lamb’s feet, which are depicted in detail in the authenticated drawing of 1592 and in Bosio’s woodcut, whilst they are merely hinted at in Chacón’s copy.

No earlier printed illustration of the apse of Old St Peter’s has been found so far that predates Antonio Bosio’s detail from 1610. In 1693, Giovanni Giustino Ciampini (1633–1698) included a copperplate engraving based on the 1592 drawing as well as the notarial certification in his work on church buildings from the time of Emperor Constantine (c. 280–337) (Fig. 15). [26]