“Yes. Wrapped in linen, or perhaps embalmed. Even popes were buried in the Catacombs. But many of the tombs were pillaged in later centuries. Bones were taken away by desecrators, or by seekers of holy relics, or for reburial. Still, some undisturbed tombs were rediscovered over the last few centuries—perhaps there are more still to find. George, this Catacomb alone encompasses fifteen miles, over four levels. And it is estimated that in all the Catacombs some half a million people were buried, over the centuries.”

Like so many numbers associated with ancient Rome, it was a stunning, impossible figure.

“Look.” She pointed to symbols, painted faintly on the walls. The light was kept low to protect the paintwork, it turned out. “Covert Christian symbols, from the days of repression and persecution. The fish you will recognize. The dove, and here the olive branch, symbolizes peace. The anchor implies resurrection. Oh, here is the famous chi-rho, formed of the first two Greek letters of Christ’s name.” It looked like the letters P and X superimposed. “And here—” Carved above one of the loculi, it was like the simple fish symbol, but two fish touched, mouth to mouth, so that it was almost like an infinity.

“What’s that?”

“The symbol of the Order.” I recognized it from my Internet search. She was studying me. “How do you feel?”

“I’m in a two-thousand-year-old graveyard. A little freaked out.”

“You aren’t worried by the enclosure? The narrow walls, the depth—you don’t feel claustrophobic?”

I thought about that. “No.”

“And if I told you I have more to show you yet—that we will go much deeper . . .”

“Are you setting me some kind of test, Rosa?”

“Yes, I suppose I am. Something about the way we talked in the café . . . You’ve reacted well so far, and I think you’re ready to see more.” She held out her hand. “Will you come? You’re free to go, whenever you like.”

By now I had come to distrust her obviously calculated touching, the overwhelming feelings it evoked in me. But I took her hand again. “What next—open sesame?”

“Something like that.”

We were standing before an innocent-looking niche, empty as the others. It had a two-fish symbol carved over it. Now, to my surprise, Rosa dug out a swipe card and passed it into a slot hidden inside the stone, up behind the fish. I glimpsed a red light, heard the unexpected humming of electronic gear.

And then, with a stony grind, a kind of trapdoor opened up beneath me—and bright light flooded up into the dusty air. I leaned forward to see. There was another staircase, but this was of polished metal, and it led down to a floor of gleaming tiles.