Page 19

“Do you actually see, or are you just agreeing with me again?”

The corner of his mouth twitched. “I see.”

She didn’t quite believe him, but she was too excited to argue. She started walking again, faster now, sweeping her lamp across the walls and the floor and the water. And now that she knew what to look for, she found it everywhere. The channel curved gently to the left, and the curve was a perfect arc. The floor dropped in a series of long, shallow steps, each one exactly as high as the one before it. Every so often there was a narrow slot cut into the wall just above the waterline. When she crouched down to peer into one, she felt a faint breath of air moving through it.

“Ventilation,” she said out loud. “Or pressure relief. Or both. God, that’s clever.”

She was talking to herself again. She knew it, and she didn’t care. Korrak followed close behind her, and every time she stopped, he stopped too, and every time she started talking, he listened.

The passage opened out into a chamber, and she forgot to breathe. It was bigger than the cavern by the falls. The stream poured into it from the channel behind them and ran across a broad, level floor of stone. Then it came to the edge of the floor and dropped, but it didn’t simply fall. It flowed down a spillway.

There was no other word for it. It was a wide, stepped slope of stone that curved gracefully down into the darkness. The water rolled over it in shallow, rippling cascades. Each step was carved with a lip along its edge, just high enough to slow the water and spread it out before it tipped over into the next one. At the bottom, far below, the water gathered in a deep basin with a soft, steady roar.

She walked slowly towards the edge. Her legs felt shaky, and it had nothing to do with the thin air.

“Energy dissipation,” she said faintly. “Every step takes some of the force out of the water, so by the time it reaches the bottom it isn’t strong enough to erode the basin. And the lip on each step spreads the flow evenly, so you don’t get channeling down the middle. Do you know how hard that is to get right?” She turned to look at him. “We build these on Earth. Or we did. They’re used for dams. But they have to be designed for a specific flow rate, and if you get the flow rate wrong, they tear themselves apart.”

He was watching her face instead of the spillway, and the warm, intent look in his eyes made her pause.

“What?” she said.

He shook his head slightly, still watching her. “Talk more.”

Heat crept up her cheeks, and she turned quickly back to the spillway, because it was a lot easier to look at than he was.

At the edge of the stepped slope, a second channel branched away to the right. It was narrower and mostly dry, but a thin trickle of water ran along the bottom of it. She followed it with her lamp as it curved away along the side of the chamber and disappeared through an opening in the wall. Where it split away from the main stream, a low stone wall crossed the channel, with a series of notches cut into the top. She knelt beside the wall and studied it for a long time.

It was an overflow. When the stream ran high, the water would rise over the notches and spill into the side channel. The extra flow would be carried safely away before it could flood the chamber. And the notches were cut at slightly different heights, so that the more water there was, the more notches it would spill through.

It was so elegant, so simple and so smart, that she wanted to laugh.

“Somebody built this,” she said. Her voice came out hushed, almost reverent. “Somebody who knew exactly what they were doing.”

She ran her hand over the top of the wall. The notches were worn smooth, softened by water, but the lines of them were still perfectly straight.

“These spillways are better than anything we’ve poured on Mars,” she said. “Korrak, who built this?”

He crouched down beside her, and for a moment he didn’t answer. He reached out and touched the stone wall, his long fingers resting lightly on the worn edge of one of the notches. His eyes softened in a way she couldn’t read. He looked sad, and fond, and a little lost.

“My people,” he said. Then, more quietly and less certainly, “I think.”

“You think?”

He touched his head the way he had the day before. “Sleeping. Some words wake. Some…” He spread his fingers helplessly, empty. “Not yet.”

She looked at the notched wall and the stepped spillway and the long, perfect channel behind them, and she tried to imagine it. His people had built this. They had cut the stone and shaped the water, so long ago that the rock had worn smooth beneath the flow.

She put her hand on the edge of the spillway, where the water slid past her fingers, cold and quick.

“This has been here millions of years,” she said softly.

“Longer than memory,” he agreed.

She didn’t realize how long she had spent exploring the chamber until her head started to swim. She’d been crawling along the edge of the spillway, looking at the joints between the steps. They were so tight she couldn’t fit a fingernail between them. She stood up too quickly, and the chamber tilted around her. Black spots bloomed at the edges of her vision. She sat down hard on the stone and pressed her mask against her face until they faded.

He was beside her in an instant, crouched close, his hand hovering near her shoulder.

“I’m fine,” she said breathlessly. “I just got excited. I forgot to go slowly.”