Quraqua had a single satellite, roughly half the size of the Moon, ash-gray, scarred, airless. Tonight it was a bright yellow crescent, friendly, luminous. Inviting. But it was a moon with a difference. Six years ago, the pilot of an incoming packet had noticed what he thought was a city high in its northern quarter. "Richard?"

He was absorbed in a hand-drawn chart spread out on his knees and across a sizable portion of the instrument panel. He waggled his hand to indicate he'd heard. "Let Henry know we're here," he said. "And make for Oz."

Beneath the red sun Bellatrix, and cloud-shrouded Quraqua, Winckelmann's shuttle Alpha (there was no Beta) glided over the moonscape. Peaks and gorges and craters merged with glare and shadow. The shuttle crossed a low mountain range and hurtled out over a sea of flat polished rock. Richard sat quietly, as he always did at such times, leaning forward against his restraints, gazing placidly out the window. Hutch was uncomfortable with his insistence on coming here first. She would have preferred to complete preparations for the evacuation before they undertook any side adventures. There would be cargo to load, and last-minute problems, and she wanted all that worked out well in advance. Instead, she could imagine Richard getting caught up in the anomaly, and adding complications.

His attitude did nothing to dispel those fears. "Plenty of time," he said. "We have until the eleventh." Five days.

A ridge appeared, swept toward them, and vanished. The mare was heavily pocked. The Guide Book, which she had posted on her overhead display, indicated it was the oldest surface area on the moon. "Some of these craters," she said, "are two billion years old."

Richard nodded, not listening. He wasn't interested in geology.

A sensor lamp blinked on.

"Ship on the scope. Henry's shuttle."

"Good." His expression warmed.

"It's about twenty minutes behind us." Hutch switched to manual, noted her position on the navigational displays, and throttled back.

"Be good to see him again." His eyes brightened. "This has to be a hard time for him. We thought we had forever to excavate Quraqua. Nobody believed we'd be ordered off. It turns out we were too cautious. Should have plowed right in. Like Schliemann."

Hutch had met Henry twice. He was an odd, rumpled little man who had given a lecture she'd attended when she was trying to learn enough archeology to persuade the Academy that she could be an asset. Two years later, when they'd shared passage on the Moon relay, he'd surprised her by remembering who she was. He even knew her name. Priscilla.

The ground began to break up into canyons. A range of needle peaks swept past.

"What were they like?" she asked. "The Quraquat?"

"They lived a long time. Individually, I mean." He fumbled in his jacket. "I should have a sketch here somewhere—must have left it in my room. Or" — sheepishly—"at home." He kept searching pockets. "They looked like furry gators. But they were warm-blooded—"

"No: I mean what were they like? What did they do? I know they had two sexes, and they had long life spans. What else?"

"They had a lot of dark ages. Not as barbarous as Earth's, not as military. But stagnant. Sometimes nothing would happen for a thousand years. No political development. No science. Nothing. They also had a talent for losing things. For example, we know of three different occasions on which they discovered Quraqua was not the center of the universe."

"Why? Why all the dark ages?"

"Who knows? Maybe we'll go through them too. We just haven't been around very long. In the case of the Quraquat,

they might have been victims of their life spans. The wrong people succeed to power and don't die. Not for a long time." He tried unsuccessfully to brush his hair out of his eyes. "Think about that. Imagine having to deal with Hart for the next sixty years." (Adrian Hart was the current chairman of the Academy Board of Trustees. He was fussy and vindictive, a micro manager with no ideas.) An amber lamp started to blink. "Coming up," she said. Sunlight danced off the rocks ahead. The reflection splintered, and raced in both directions across the plain. They might have been looking at an illuminated highway, bright, incandescent.

Richard leaned forward expectantly. The light grew solid. It became a wall. Bone-white against the gray moonscape, it extended from a low range of hills on the south to the horizon on the north. Hutch throttled back, fired a series of quick bursts from the maneuvering rockets. She took them down near the surface.

The wall grew, and began to crowd the sky. It was enor-mous. The scale of the thing, as they drew closer, reminded her of the old textbook representations of Troy. She powered up the scopes, put the picture on the monitors: the thing appeared to be seamless.

Except that there were holes punched in it. Long sec-tions had fallen away, and there were places where the wall appeared to have been hammered into the ground. Rubble lay along its base.

"Look," Richard said. The structure was seared, scorched. "It does look as if somebody tried to knock the thing down."

"One would almost think so." "What kind of fire would burn out here?" "Don't know." He folded his arms and canted his head. "I was wrong to neglect this place all these years. This is a fascinating site." "So what happened here?"

"I have no idea." He sat looking for several minutes. "Frost," he said.

"Say again?"

"I keep thinking of Robert Frost. 'Something there is that doesn't love a wall— " He sank back, placed his fingertips together, and let the moment wash over him. "Magnificent," he breathed. "An utterly sublime mystery. It is really no more than a rock sculpture in an airless place. Why was it built? And who would assault it?"

It towered over them.

The only reasonable explanation was that it had been hit by a swarm of meteors. There was indeed meteoric rock in the area. And a lot of craters. But there seemed something purposive in the assault.

"It's probably an illusion," said Richard, who seemedalways able to read her thoughts. "It's the only artificial structure out here, so there's nothing to contrast it with except the random chaos of the moonscape. Still—" He shook his head. "It's hard to know how to read this."

It had been built, Hutch knew, between eleven and twelve thousand years ago. "Its age matches the Tull set."

"Yes," he said. "There may be a connection."

It was eerie, and she found herself scouring the plain for oversized footprints.

The wall was 41.63 meters high, and 8.32 kilometers on a side. It enclosed a perfect square. "The length of a side," she read off the display on the monitor, "is precisely two thousand times the height."

"Base ten," said Richard.

"How many fingers did the Quraquat have?"

"They weren't exactly fingers. But four."

"The Monument-Makers had five."

The shuttle nosed up to the wall. It hovered a few meters away. "Do we want to land?"

"No. Not out here."

The wall had been old before there were pyramids in Egypt. Hutch floated before it, and felt the transience of her own mayfly existence as she never had on lapetus, or at the other ancient sites. She wondered what the difference was. Maybe it is bracing, encouraging to know that beauty somehow survives. But to be outlived by such primal madness—

"This thing," said Richard, "is so different from everything else they left. If it is indeed theirs. The Monuments are light, exquisite, elegant. The race that created them enjoyed being alive. This thing: it's grim. Irrational. Ugly. A fearful creation." He pushed back in his chair the way people do during a simmy when the werewolf is approaching. "Take us up," he said.