Almost everything the general reader knows about the Roman catacombs is nineteenth-century fiction, and the truth is more interesting.
They were not hiding places
The popular image (persecuted Christians sheltering underground, holding secret Masses by lamplight, using the fish as a covert password), comes largely from Victorian devotional literature and the novels that followed it. It does not survive contact with the evidence.
- The catacombs were not secret. Their entrances were on public roads and their existence was perfectly well known to the authorities, which is precisely why they were confiscated during the persecutions of the third century.
- They were not habitable. They are narrow, unventilated, and full of decomposing bodies. Nobody lived there.
- They were not exclusively Christian as a technique. Rome's Jewish community used identical methods at Vigna Randanini and Villa Torlonia, and the Jewish catacombs are in places earlier than the Christian ones.
The actual reason for digging is prosaic. Roman law forbade burial inside the city walls; land above ground outside them was expensive; the tufa around Rome is soft enough to cut with hand tools and stable enough to hold a gallery without shoring. Going down was simply the cheapest way to bury a great many people.
What they were
They were cemeteries, and then they were shrines.
The dead were laid in loculi, shelves cut into the gallery walls and sealed with tile or marble. Wealthier families cut out cubicula, small chambers, and decorated them. Christians preferred burial to the cremation then usual among Romans, which is a doctrinal difference about the body made visible in the archaeology.
Above all, people came back. The refrigerium, a commemorative meal eaten at the grave on the anniversary, was an ordinary Roman practice that Christians continued, and the small tables and benches cut for it survive. Augustine records his mother Monica's habit of it and Ambrose's discouragement of it.
The art
The catacombs hold the earliest substantial body of Christian art, and what it shows is popular faith rather than official theology: what ordinary people wanted painted over their relatives:
- the orant, a figure standing with arms raised in prayer
- the Good Shepherd, a young man with a sheep across his shoulders, borrowed wholesale from pagan pastoral imagery
- the fish, the anchor, the dove
- Jonah, Noah, Daniel, Susanna, the raising of Lazarus: deliverance stories, almost without exception
The inscriptions are in poor Greek and worse Latin, frequently misspelled, and are overwhelmingly about grief and reunion rather than doctrine.
Rediscovery
The catacombs were visited as shrines through late antiquity, progressively emptied of their more famous relics from the eighth century as those were translated into churches inside the walls, and then largely forgotten. Antonio Bosio began systematic exploration around 1600. Giovanni Battista de Rossi, in the nineteenth century, identified the crypt of the popes in San Callisto and established the methods that made Christian archaeology a discipline rather than a treasure hunt.
They remain the property of the Holy See, administered by the Pontifical Commission for Sacred Archaeology, and Mass is still occasionally celebrated in them, which is the one part of the Victorian picture that is now, in a modest way, true.