During excavations performed in the 19th century, a series of Ancient Roman rooms were discovered under the nave of the church. Some of these rooms date back to the first and fourth centuries AD. According to the writer
Charlotte Anne Eaton, these rooms were dens that were part of a
vivarium in which wild animals were kept before being used in entertainments held at the
Colosseum. A low vaulted passage connected this vivarium with the Colosseum. The underground sites of the basilica were discovered in 1887 by Father Germano da San Stanislao, who at the time was rector of the Basilica, and was searching for the tombs of the martyrs John and Paul. He found twenty decorated rooms belonging to at least five different buildings dated between the first and the fourth century AD. These five buildings comprise one of the best conserved Roman era residential building complexes still in existence today, and one of the best examples of a
domus ecclesiae ("house church"). The original
frescoes can still be seen, with scenes of the martyrdom. The houses are accessed outside the church on the
Clivus Scauri. In one room, which was a nymphaeum courtyard, an elegant third-century AD fresco depicting
Proserpine and other divinities among cherubs in a boat () can be found, as can traces of another marine fresco and mosaics in the window arches. Between the third and the fourth century AD, some modifications were made to the rooms, and a sort of oratory was made, with Christian-themed frescoes, while in the other rooms the decorations did not specifically have Christian themes (winged genies, garlands, birds, etc.). A
confessio was also built in the fourth century AD in a passageway behind the Clivus Scauri. The walls of the
confessio were frescoed with Christian themes (e.g., the beheading of Saints
Crispus, Crispinus, and Benedicta, female figures and an
orante or "person in prayer"). ==References==