Orphans of the Void by Michael Shaara - Finding a cause worth dying for is no great trick-the Universe is full of them. Finding one worth living for is the genuine problem!

In the region of the Coal Sack Nebula, on the dead fourth planet of a star called Tyban, Captain Steffens of the Mapping Command stood counting buildings. Eleven. No, twelve. He wondered if there was any significance in the number. He had no idea.

"What do you make of it?" he asked.

Lieutenant Ball, the executive officer of the ship, almost tried to scratch his head before he remembered that he was wearing a spacesuit.

"Looks like a temporary camp," Ball said. "Very few buildings, and all built out of native materials, the only stuff available. Castaways, maybe?"

Steffens was silent as he walked up onto the rise. The flat weathered stone jutted out of the sand before him.

"No inscriptions," he pointed out.

"They would have been worn away. See the wind grooves? Anyway, there's not another building on the whole damn planet. You wouldn't call it much of a civilization."

"You don't think these are native?"

Ball said he didn't. Steffens nodded.

Standing there and gazing at the stone, Steffens felt the awe of great age. He had a hunch, deep and intuitive, that this was old-too old. He reached out a gloved hand, ran it gently over the smooth stone ridges of the wall. Although the atmosphere was very thin, he noticed that the buildings had no airlocks.

Ball's voice sounded in his helmet: "Want to set up shop, Skipper?"

Steffens paused. "All right, if you think it will do any good."