Here, then, was a basilica or church discovered in the midst of a catacomb. That the latter belonged to Flavia Domitilla was well known; and yet another proof, which illustrates archæological difficulties and the method of overcoming them, was found here. It was a broken slab of marble containing a portion of an inscription:
......RVM
.....ORVM
(*)
and having the image of an anchor at the point(*). It was concluded that the anchor was placed at an equal distance from both ends of the inscription, and the discoverer, with the knowledge he already has of the place, supplied the letters which he considered wanting to the completion of the inscription, and thus produced the words,
SEPVLCRVM
FLAVIORVM
*
(sepulchre of the Flavii). This reading is very probably the right one, and its probability is greatly strengthened by the position of the anchor, since the full inscription, as here shown, leaves that sign still in the centre.
But to find the name borne by these ruins when the building of which they are the sole remnants was fresh and new presented a task to their discoverer. It was necessary to seek in ancient works—pontifical books and codices—for some account of a basilica on the Ardeatine Way. In the life of S. Gregory the Great it is related that this pontiff delivered one of his homilies “in the cemetery of S. Domitilla on the Ardeatine Way, at the Church of S. Petronilla.” The pontifical books and codices, although they differ in details—some saying in the cemetery of Domitilla, and others in that of Nereus and Archilleus, which is the same place under another name—agree in the principal fact. On the small remnant of plaster remaining on the wall of the apse an unskilled hand had traced a graffito, or drawing scratched on the plaster with a pointed instrument, somewhat resembling those found on the walls of Pompeii. This graffito represents a bishop, vested in episcopal robes, seated in a chair, in the act of delivering a discourse. This rude sketch of a bishop so occupied, taken in conjunction with the fact that S. Gregory did here deliver one of his homilies, is a link in the chain of evidence which identifies the ruin with the ancient basilica of S. Petronilla.
But a still more convincing testimony was forthcoming. A large fragment of marble, containing a portion of what appeared to have been a long inscription, was found in the apse. There were but few complete words in this fragment, and these were chiefly the termination of lines in what seemed to have been a metrical composition. Odd words, selected at random from a poem, standing alone, devoid of preceding or succeeding words, might not seem to furnish very rich materials even to an archæologist. These wandering words were, however, recognized to be the terminal words of a poem or eulogium written by Pope Damasus in honor of the martyrs Nereus and Achilleus. Now the connection between this metrical eulogium and the basilica was to be sought for. In the Einsiedeln Codex the place where this poem was to be seen is stated to have been the sepulchre of SS. Nereus and Achilleus, on the Appian Way, at S. Petronilla. The poem, or rather this fragment of it, being found at this sepulchre, it was natural to conclude that the church was that of S. Petronilla. The Appian Way is the great high-road from which the Ardeatine Way branches off near this spot.
Again, the basilica of S. Petronilla was frequented by pilgrims from many nations in the VIIth century. Among these were Gauls, Germans, and Britons. In their itineraries of the martyrs’ sepulchres in Rome, and in the collection of the metrical epigraphs written at these places, it is proved that the original name of this church was that of S. Petronilla. “Near the Ardeatine Way is the Church of S. Petronilla,” say these old documents, and they likewise inform us that S. Nereus and S. Achilleus and S. Petronilla herself are buried there: “Juxta viam Ardeatinam ecclesia est S. Petronillæ; ibi quoque S. Nereus et S. Achilleus sunt et ipsa Petronilla sepulti.”
A second fragment of the slab containing the metrical composition of Pope Damasus has since been found, and this goes to confirm the testimony furnished by the former fragment. In the following copy of the inscription the capital letters on the right-hand side are those on the fragment first discovered; those on the left belong to the recently-discovered portion:
“Nereus et Achilleus Martyres.