A person blocked the flow of air, consumed its vital goodness, and pumped a lot of heat into it besides. So you could improve the flow of air into a problematic region by simply evacuating the passageways around it and moving the people somewhere else. You could likewise cool an area by taking out its people—or warm it up, by crowding more people in. It was impossible to solve every problem by “huddling.” The kitchens, and the nursery and crèche where the Order’s babies were cared for en masse, were a constant difficulty. But on the whole, with careful monitoring and analysis, the system worked well, and was becoming increasingly effective as they learned.

Of course there were many grumbles at this regime of constant shifting, but people had adapted. Space had been at a premium from the beginning, so you weren’t allowed to bring a great deal of personal baggage into the Crypt in the first place. And furniture in each dormitory room was becoming uniform, so it made no real difference where you were.

As far as Regina was concerned, this constant uprooting was an unexpected side benefit. Regina wanted every sister to think of the whole Crypt as her home, not just her own little corner of it.

Meanwhile Order members began to spend an increasing amount of time underground.

In the Crypt there was no summer or winter, and no threats from barbarians or bandits, and no disease, as all the food and water was clean. And it was safe in here, safe and orderly in a world that was becoming increasingly threatening. To the children who had been born here, in fact, it was the aboveground world that seemed strange—a disorderly place where the wind blew without control and water just fell from the sky . . .

One day, Regina mused, somebody would be born in the Crypt, would live out her whole life underground, and then die here, her body being fed to the great ventilation furnaces, a last contribution to the Order. Regina would not live to see it happen, but she was sure that grand dream would soon be fulfilled.

Regina met Ambrosius Aurelianus seven days later. He stood in the Forum, listening to an orator who declaimed the ruin of the world to a cheerful crowd. He wore the leather armor of a Celtae warrior, even here in the heart of Rome. Ambrosius had aged, but he was much as Regina remembered—the stocky frame, the sturdy, determined face. His startling blond hair was receding, and a deep scar disfigured one side of his face. But his blue eyes held the same warm zeal she remembered from Artorius’s war councils, all those years ago in Londinium.

He greeted her with clumsy gallantry, insisting she hadn’t changed.