, a modern copy of which (1860) is
to be seen on the side of the mosaic in the apsidal arch. The poem
relates how the hill of Cyriaca was cut away, and how, in consequence
of the excavation, the church became light, accessible, and free from
the danger of landslips and inundations. The importance of the work of
Pelagius is rather exaggerated by the composer of the poem. The church
was never free from dampness and want of air and light until the
pontificate of Pius IX., who cut away another section of the hill.

The damage done to the catacombs by the builders of these sunken
basilicas is incalculable. Thousands of graves must have been
sacrificed for the embellishment of one.

* * * * *

The reader cannot expect to find in these pages a description of this
class of basilicas; that of S. Peter's alone would require several
volumes. I have in my modest library not less than twenty-two volumes
on the subject, an insignificant fraction of the Petrine literature.
And what do we know about S. Peter's? Very little in comparison with
the amount of knowledge that lies yet unpublished in the volumes of
Grimaldi,[69] in the archives of the Vatican, in epigraphic,
historical and diplomatic documents scattered among various European
libraries.

The history of the building has yet to be written. Duchesne's "Liber
Pontificalis" and de Rossi's second volume of the "Inscriptiones
Christianae" provide the necessary foundations for such a work. Let us
hope that the Vatican will soon find its own Rohault de Fleury.[70]

The following sketch of the origin of the two leading sacred edifices
of Rome may answer the scope of the present chapter. But let me repeat
once again the declaration that I write about the monuments of ancient
Rome from a strictly archaeological point of view, avoiding questions
which pertain, or are supposed to pertain, to religious controversy.
For the archaeologist the presence and execution of SS. Peter and Paul
in Rome are facts established beyond a shadow of doubt by purely
monumental evidence. There was a time when persons belonging to
different creeds made it almost a case of conscience to affirm or deny
_a priori_ those facts, according to their acceptance or rejection of
the tradition of any particular church. This state of feeling is a
matter of the past, at least for those who have followed the progress
of recent discoveries and of critical literature. However, if my
reader