Catacomba dei Due Felici is a lost set of catacombs on the Via Aurelia, though to be around the junction with the Via del Casale di San Pio V. This is in the Aurelio quarter.
The basilica here was founded by Antipope Felix II (355-7).
His context was the Arian Controversy during the reigns of Pope Liberius and Emperor Constantius II. Pope Liberius was exiled for two years from 355, and replaced by Felix. The true pope was recalled by popular demand, and the antipope then retired to a residence on the Via Portuense until he died in 365.
His residing on the Via Portuense is mentioned in the Passio Felicis, and this might be a factual statement in a document that is otherwise romantic fiction. From it derives the myth that Felix fell out with the emperor, refused to subscribe to Arianism and was hence martyred. This mythologising had a very long pedigree, as the liturgical veneration of the antipope in the Roman calendar only ceased in 1962. This was despite scholars pointing out the problem from the 16th century.
The source of the Passio, and the motivation for writing it, are both unknown although a scholarly guess is that it derived from a monastery on the Via Portuense attached to the shrine at the Catacomba di San Felice ad Insalsatos on the Via Portuense. It seems that the Felix being venerated there in the early Middle Ages was the antipope, but it seems more likely that he supplanted an earlier unknown martyr than that his veneration was created completely from scratch.
Later history Edit
The basilica and catacombs was on the pilgrimage circuit in the early Middle Ages. It was listed as the third destination on the Via Aurelia, after San Pancrazio and Catacomba dei Santi Processo e Martiniano but before Catacomba di Calepodio.
The title of Due Felici is a puzzle that has exercised scholars for centuries. The tradition was that the two Felixes were two popes, Pope Felix I and Antipope Felix II. The problem with this was that the former was buried at the Catacombe di San Callisto. The latter might have been buried here, or on the Via Portuense.
A neat but completely unprovable solution to the dilemma is that there was an unknown martyr called Felix on the Via Portuense, two of them on the Via Aurelia and then two popes called Felix who were very thoroughly confused with the three of them.
Speculation as to the location of the shrine has focused on the present Via Aurelia Antica between the Via Leone XIII overbridge and the junction with the Via del Casale di San Pio V.
For example, Kirsch writing in 1946 ("The Catacombs of Rome") mentions "the entrance to an ancient stair, which communicates with a small network of badly ruined cemeterial galleries". This was in the then Vigna Pellegrini, north of the road.
However, the location will only ever be fixed if someone finds the foundations of the church, or an epigraph mentioning a Felix or two. Don't hold your breath.