The catacombs hold a very interesting place in the romantic tradition about how early Christianity developed. It's often been suggested that these were great hiding places, and the Christians would go down in the catacombs to worship during periods of persecution. But really there weren't that regular kinds of persecution going on, and even when we find larger rooms or chambers in the catacombs, they weren't used for regular worship. Churches didn't go down in there to hold Eucharist and assembly on a regular basis. So, what were these rooms used for? Why did they have benches lining the walls, what looked like places where you could hold eucharistic assembly? The answer is, they're holding meals for the dead. We know, in fact, from a number of sources, Christian and non-Christian alike, that the funerary meal, a kind of picnic with the dead, was something that most families practiced in the city of Rome. So, we have to imagine as part of their daily life, as part of their regular activity, Christians, just like their pagan neighbors, going down into the catacombs to hold memorial meals with dead members of their families.
Most of the catacombs are found in Rome where they number nearly sixty, while the same number can be counted in Latium. In Italy, the catacombs developed especially in the South where the soil consistency is harder but at the same time more ductile for excavation. The northernmost catacomb is the one that developed on the Island of Pianosa, while the southernmost cemetery hypogea are the ones in northern Africa and especially at in Tunisia. Other catacombs are found in Tuscany (Chiusi), Umbria (near Todi), Abruzzi (Amiterno, Aquila), Campania (Naples), Apulia (Canosa), Basilicata (Venosa), Sicily (Palermo, Siracusa, Marsala and Agrigento), and Sardinia (Cagliari, S. Antioco).
And now this mysterious discovery of Quintus Claudius in the catacomb with the Nazarenes!
In the Roman catacombs the most ancient image is preserved of Our Lady who is depicted in a painting in the cemetery of Priscilla on the Via Salaria. The fresco, which can be dated back to the first half of the third century, depicts the Virgin with the Child on her knees in front of a prophet (perhaps Balaam or Isaiah) who is pointing to a star to refer to the messianic prediction. In the catacombs other episodes with Our Lady are also represented such as the Adoration of the Magi and scenes from the Christmas crib, but it is thought that prior to the Council of Ephesus, all these representations had a Christological and not a Mariological significance.
This is what they were. They were not hideouts, they were not places where Christians were hiding. They were quite public, where everyone was being buried of this class. So, Christians were being buried in the catacombs. If they were able economically to do more than simply bury their dead, if they could put an image there, for example, a picture, you began to get scenes. First of all, you got symbols like the anchor or the dove; that would be sort of the simplest one. Then you could get scenes like, say, the philosopher or the woman with her hands raised in prayer, the symbol of piety; various scenes, or you could get literally biblical stories.