How the Rome Catacombs Were Dug
Kilometres of gallery, several storeys deep, cut by hand with no shoring and still standing after eighteen centuries. The answer starts with the rock.
The rock that made it possible
Rome sits on tufa, a soft volcanic rock laid down by the Alban Hills. It has two properties that matter here. It cuts with a hand pick, so a two-man team could open metres of gallery in a day. And it hardens on contact with air, so a passage stiffens into something close to masonry once it is exposed.
That combination is why the galleries need no props and no lining. Cut the same corridors into sand and they collapse; into hard stone and nobody could afford them. The catacombs exist because the ground under Rome happens to be exactly the right material.
Cut by hand: the fossores' method
The sequence was the same on every site, and you can still read it in the walls as you walk.
- Sink a stair. A stepped shaft from the surface, wide enough for two, giving light and air to the level below.
- Drive a gallery. A corridor about a metre wide and tall enough to stand in, following the seam of workable tufa.
- Cut the niches as you go. Graves were opened in the walls of the corridor while it advanced, not afterwards.
- Go deeper, not wider. When a level filled, the fossores cut a new stair and began a second beneath it, then a third.
- Seal and mark. Each grave was closed with tile or marble, mortared, and often scratched with a name and a symbol.
Loculus, cubiculum, arcosolium
Three words cover almost everything you will see, and a guide will use all of them.
| Form | What it is | Who got one |
|---|---|---|
| Loculus | A rectangular niche cut into the corridor wall and sealed with tile or marble | The standard grave, stacked up to five high |
| Cubiculum | A small chamber opening off the gallery, with niches on three sides | A family, who paid for the room |
| Arcosolium | An arched recess over a tomb chest, the curve above it plastered and painted | Wealthier burials; most surviving painting is here |
| Forma | A grave cut into the gallery floor and covered with a slab | Later burials, once the walls were full |
The loculi are what you will remember: rows of empty rectangles running away into the dark on both sides, at head height and above it and below it.
Four levels down, and why you only see one
The larger sites descend through several levels, the earliest nearest the surface and the latest deepest, which is the reverse of what most people expect. San Callisto's network runs for kilometres across its levels; Domitilla's is measured in the same terms.
Visitors see a lit, consolidated section of a single level. The rest is closed for conservation, and the reason is prosaic: breath and body heat raise the humidity, and humidity takes the paint off the walls. The restriction is what keeps the paintings there at all.
Light, air and finding your way
The fossores worked by oil lamp, and niches for lamps are cut beside the graves at intervals along the corridors. Vertical shafts called lucernari were opened to the surface at intervals, bringing daylight and air into the deeper galleries — you will pass under one or two and feel the temperature change.
Navigation was by memory and by the graves themselves. There are no signs and no logic to the plan beyond the seam of workable rock. Modern electric lighting follows the visitor route only; a metre past it, the dark is complete.
The paintings, and what they are made of
The earliest Christian art anywhere is on these walls, in earth pigments applied fast onto fresh plaster. The repertoire is small and consistent: the Good Shepherd carrying a sheep; orant figures standing with arms raised; banquet scenes; Jonah, Daniel and Lazarus, read as promises of rescue. Colours are ochre, red and green, because those pigments were cheap and stable.
Much of it is faint, and a guide's lamp is what makes it legible — one of the concrete arguments for a guided departure over a ticket. You can see what survives on the gallery, read what a visit feels like on what to expect underground, and open Rome Catacombs Tours for the departures that reach the painted chambers.