Santi Giovanni e Paolo al Celio

Interior

The inside has three naves, with pillars joined to the original columns. The altar is built over a bath, which holds the remains of the two martyrs. The apse is frescoed with Christ in Glory (1588) by Cristoforo Roncalli (one of the painters called il Pomarancio); while below this fresco are three paintings: a Martyrdom of St John, a Martyrdom of St Paul, and the Conversion of Terenziano (1726) by Giovanni Domenico Piastrini, Giacomo Triga, and Pietro Andrea Barbieri respectively.

The sacristy features a canvas by Antoniazzo Romano of the Madonna and Child with Saints John the Evangelist and John the Baptist, and Saints Jerome and Paul.

Cardinalatial title

The basilica is connected with the cardinalatial Titulus Ss. Ioannis et Pauli. Among previous Cardinal Priests of this title are three who became Pope: Pope Honorius III (Cencio Savelli, elevated to cardinal in 1198), Pope Adrian VI (Adriaan Boeyens, elevated to cardinal in 1517) and Pope Pius XII (Eugenio Pacelli, elevated to cardinal in 1929). Since Francis Spellman became the new Cardinal Priest of the titulus in 1946 (after it had been vacated by Pacelli's election to the papacy in 1939), it was held until 2015 by cardinals who were Archbishops of New York. In 2012, Archbishop Timothy Dolan of New York was elevated to cardinal and assigned a different title, because Cardinal Edward Egan, the first prelate to enjoy the title of Archbishop Emeritus of New York, continued in the title of Ss. Ioannis et Pauli until his death on 5 March 2015. The title is now held by Cardinal Josef De Kesel, the Archbishop of Mechelin-Bruxelles, who was appointed to it on 19 November 2016.

Excavations

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 (3 m × 5 m (9.8 ft × 16.4 ft)) 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").