"All of us here have level two security; we are aware the Stoners were humans, and that they came from a culture remarkably similar to our own. In fact, they come from a future version of the Earth. We know that there were at one time two major social categories: the Geshels, or technically and scientifically oriented peoples, and the Naderites. I'm wondering, by the way, who's going to tell Ralph about this."

Weary laughter from the audience. "Old joke," Takahashi whispered to Patricia.

"We now know that Alexandria, before the exodus of the Stoners, was occupied largely by orthodox Naderites. They seemed to cling to technologies and styles predating the twenty-first century."

Patricia, with something of a jolt, realized none of these people except herself, Takahashi and Rimskaya would know the reason why that particular dividing line was important.

"In this way, they were something like the Amish. And like the Amish, they made concessions—the megas and other architectural innovations among them. But their aim was clear; they chose to retain the style of Alexandria and rejected the more advanced style of Thistledown City. We are not at all sure when this division of the orthodox Naderites and their more liberal fellows and Geshels occurred, but it was not early in the Stone's voyage.

"We are fairly certain now that Thistledown City had been evacuated and locked up at least a century before Alexandria. In other words, the exodus had occurred in the third chamber almost a hundred years before the final evacuation of the second chamber. There is substantial evidence that the second chamber was finally emptied by force.

"The Stone was emptied, then, not simply because of a mass social migration, but to fulfill a definite plan. The people behind the plan apparently gave their more conservative fellows a century to comply, and when they still proved reluctant, moved them out against their will. Oddly enough, we have evidence that some of the orthodox Naderites were forced to live in Thistledown City for a few years.

"We assume that all the Stoners exited by way of the corridor. We have no physical proof of this, and no knowledge yet why the exodus occurred, or why the powers behind the exodus wished the Stone to be completely deserted."

The presentation ended with a series of projected pictures showing living quarters in Alexandria and diagrams of theorized population levels for different centuries in the second and third chambers. To scattered applause, Rainer returned the lectern to Rimskaya.

"The anthropology and archaeology groups have done a wonderful job, don't you agree?" he prompted, gesturing to those in the front row of seats.

Patricia stood as there was more applause. Takahashi followed her out of the cafeteria and into the tubelight.

"That's fascinating," she said, "and I appreciate the tour today. They're working in the dark, aren't they?"