But there were few loculi, I would learn, because members of the Order were never alone: the bigger the room, the bigger the crowd, the better.

The deeper in we penetrated, the more powerful that animal smell became. It was like walking into a lion’s cage.

I tried to keep a clear head. “The workers here seem young,” I said. “Nobody much over twenty-five or thirty?”

“Actually, most people here are older than that.”

“They don’t look it …”

“There are some youngsters, of course. Everybody has to learn. But most of the Order’s younger members work downbelow.”

“Downbelow?”

“On the lower levels.”

“There are lower levels ?”

We passed through a domain of libraries. The books were densely packed, and, as you see in some academic archives, the shelf units ran on rails: in a whole room there would be only enough space for a single passageway between a pair of shelves, and you would have to turn a little handle to make the shelves roll back and forth until you got the access you wanted. There was a lot of material. Farther on there were rooms more like museum departments, which contained what looked like extremely ancient manuscripts, scrolls and clay tablets, all held in air-conditioned isolation and low light, many of them in the drawers of glass-topped cabinets.

This area was the scrinium, said Rosa, the Order’s term for the monumental internal record center that had now been turned outward to fuel the Internet genealogy business. Rosa showed me cabinets full of somewhat dog-eared index cards. There was so much material, she said, that even the indices had an index. We passed a computer center, where great mainframes hummed behind sealed windows. I got a fresh sense of the power and wealth of this place.

Before we left the scrinium Rosa gave me a small hardback book. It turned out to be the story of Regina, our Roman British ancestress — “A more complete biography than of anyone else in the ancient world, even the Caesars,” Rosa said. “Bedtime reading.”

A little farther on, to my surprise, we came to classrooms, where children, mostly girls, sat in neat rows, or worked in groups at desks, or labored over baffling-looking experiments in a science.

Rosa told me that few of these pupils belonged to the Order. Offering quality education to outsiders had been the Order’s earliest significant money earner — earliest in the Order’s terms, I learned, meaning ‘fifth century after Christ.’ She said they even had accounting records that went back that far, though the earliest entries were of limited use: they predated the invention of the double-entry bookkeeping system by the best part of a millennium.

“How inconvenient,” I murmured.

In one place there was even a small theater, where a group of young teenagers was rehearsing a play.

Schools. A theater. A play. And all of this, remember, dug deep into the ground below four levels of Catacombs.

Again we walked on.

In that first visit I didn’t even come close to figuring out the geography of the Crypt. The place isn’t designed to give you long vistas and perspectives anyhow; it’s designed to disorient, to make you forget where you are.

I would discover later that the Crypt was organized on three great levels. But each of those levels was subdivided by intermediate floors and mezzanines. The layout was functional, and changed all the time according to need, the arbitrary divisions between compartments blurring. All that helped mix up the geography in everybody’s heads, of course. I certainly didn’t figure out, that first time, how far those branching corridors and mushrooming chambers led; I never came to anything that could have been an outside wall, a layer of tufa like that I had seen carved out in the Catacombs above. Even so, I could see that the Crypt was immense.

And it was full of people. That was the one thing that struck me every second.

They were all around me, all the time, everywhere we walked. They all seemed similar, all smooth-faced and ageless, all of a compact, rounded build — and not tall; I was one of the tallest there, so I was seeing over the heads of the crowd. I was immersed in touch constantly: they would brush against me, and sometimes one would rest a hand on my shoulder as she squeezed past. There was that smell, the overall leonine stink of the compound, but something subtler when one of them came close, the milky sweetness I had noticed about Rosa.

And then there were the faces. It took me some minutes, after entering that first corridor, to recognize how similar they all were. They were all like Rosa, and therefore like me, almost all of them with oval faces, broad, flat noses — and the slate-gray eyes that have been a family trait for generations. They were all around me, faces like mirrors of mine — if younger, smoother, happier. There was a constant racket, but nobody seemed to be shouting, arguing, barging past anybody else; everybody was busy, but nobody was rushing or stressed out. Despite the hubbub, there was a great sense of order about the place.

I felt confused, baffled, battered by astounding impressions. But, odd though it seems, I didn’t feel uncomfortable. I’ve always been drawn to order, regularity — not control, necessarily, but calm. And this place, for all its unfamiliarity and surface strangeness, was at heart a deep well of calm; I could sense that immediately.

What I felt was: I belong here.

Rosa brought me to a kind of balcony. It was a rare viewpoint offering a cutaway view of at least some of the Crypt, like looking down into a shopping mall from a top level. Rosa pointed out a row of open- roofed chambers lined with bunk beds: dormitories. Farther away was a blocky structure that was a hospital, she said. People were everywhere I looked, moving, working, interacting with each other in little knots.

“There must be—” I waved a hand at the teeming masses below. “ — a control center. Some kind of management structure.”

“No control center. No bridge on this great underground submarine.” Rosa was watching my face. “How do you feel now? Are you thinking about all the rock over your head? Do you feel shut in, lost?”

“I’m in an underground city, by God,” I said. “I have to keep reminding myself that all this is dug into the ground under a Roman suburb … You know, I still haven’t got you in focus, Rosa.”

She wasn’t fazed. “But the Order is me. I told you, it’s my family — and yours. If you can’t see that, you can’t see anything about me.” She waved her hand. “George, do you blame our parents, Father, for my being sent away — for this peculiar gap in your life?”

I frowned. “I’m not sure.”

“ I don’t blame them,” she said definitely. “They did what they had to do to enable the family to survive. I understand that now, and I think I understood it even as a child.” I wondered if that could be true. “And besides, look around you. I’ve hardly suffered by being sent here.”

Suddenly I felt resentful. I hadn’t come here to see this vast subterranean city, after all, but her. And she seemed barely perturbed by my presence. This wasn’t enough of a reaction for me, emotionally. I wanted to break down her complacency — to make her see me.

Harm may not have come to her. But harm has come to me, I thought.

I had no idea how long I had been down there. At last, something prompted me to get out of there.

Rosa didn’t protest. She escorted me back along that long corridor, back to the anteroom, and then up to the Catacombs. We climbed alone, in the perpetual darkness, up the levels, before ascending that last staircase and emerging from the Catacomb’s gloomy entrance.