The Ringworld Engineers

by Larry Niven

  Chmeee said, “The vacuum suits and the Grass Giant’s armor show their shape: humanoid, but with enlarged joints and a face pushed forward. There is more proof. We’ve met so many hominids, all different. They had to be derived from a common ancestor: your own ancestor, the Pak breeder.”

  “Sure. It’d also tell us how Prill died.”

  “Does it?”

  “Boosterspice was tailored for the metabolism of Homo sapiens. Halrloprillalar couldn’t use it. She had her own longevity drug, and it could be used by a number of species. It struck me that Prill’s people might have made it from tree-of-life.”

  “Why?”

  “Well, the protectors lived thousands of years. Some factor of tree-of-life, or a subcritical dose of it, might trigger just enough of the change to do that for a hominid. And the Hindmost says Prill’s supply was stolen.”

  Chmeee was nodding. “I remember. One of your asteroid mining craft boarded the abandoned Pak spacecraft. The oldest man in the crew smelled tree-of-life and went mad. He ate beyond the capacity of his belly, and died. His crewmates could not restrain him.”

  “Yeah. Now, is it too much to expect that the same thing happened to some UN lab assistant? Prill walks into the UN building carrying a flask of Ringworld longevity drug. The UN wants a sample. A kid barely too young for his first dose of boosterspice—forty, forty-five—opens the flask. He’s got the eyedropper all ready. Then he gets a whiff. He drinks it all.”

  Chmeee’s tail lashed air. “I would not go so far as to say that I liked Halrloprillalar. Still, she was an ally.”

  “I liked her.”

  The hot wind blew around them, filled with dust. Louis felt harried. They wouldn’t get another chance to talk in privacy. The probe that relayed signals to and from Needle would soon be too high up the Arch for this kind of trick to work.

  “Can you think like a Pak for me, Chmeee?”

  “I can try.”

  “They put maps all over the Great Oceans. Instead of mapping Kzin and Down and Mars and Jinx, can you tell me why Pak protectors wouldn’t just exterminate the kzinti and Grogs and martians and bandersnatchi?”

  “Uurrr. Why not? The Pak would not flinch at exterminating alien species, according to Brennan.”

  Chmeee paced as he mulled the problem. He said, “Perhaps they expected to be followed. What if they lost a war; what if they expected the winners to come hunting them? To the Pak, a dozen burnt-out worlds within a dozen light-years of one another might indicate the presence of Pak.”

  “Mmm ... maybe. Now tell me why they’d build a Ringworld in the first place. How the futz did they expect to defend it?”

  “I would not attempt to defend a structure so vulnerable. Perhaps we will learn. I have also wondered why Pak would come to this region of space in the first place. Coincidence?”

  “No! Too far.”

  “Well?”

  “Oh ... we can guess. Suppose a lot of Pak wanted to run as fast and as far as they could. Again, say they lost a war. Got kicked off the Pak world. Well, there was one safe route out into the galactic arms, and it was mapped. The first expedition, the one that settled Earth, got to Sol system without running into any danger they couldn’t handle. They sent back directions. So the losers followed them. Then they set up shop a good safe distance from Sol system.”

  Chmeee mulled that. Presently he said, “However they came here, the Pak were intelligent and warlike xenophobes. That has implications. The weapon that vaporized half of Liar, the weapon you and Teela persisted in calling a meteor defense, was almost certainly programmed to fire on invading ships. It will fire on Hot Needle of Inquiry or the lander, given the chance. My second point is that the Hindmost must not learn who built the Ringworld.”

  Louis shook his head. “They must be long gone. According to Brennan, a protector’s only motivation is to protect his descendants. They wouldn’t have let mutations develop. They’d never have let the Ringworld start sliding into the sun.”

  “Louis—“

  “In fact they must have been gone hundreds of thousands of years. Look at the variety of hominids we’ve found.”

  “I would say millions of years. They must have departed soon after the first ship called for help, and died soon after completing the structure. How else would all of these varieties have had time to develop? But—“

  “Chmeee, look: suppose they finished the Ringworld a mere half million years ago. Give the breeders a quarter of a million years to spread out, with the protectors fighting no wars because the territory’s virtually unlimited. Then let the protectors die off.”

  “From what?”

  “Insufficient data.”

  “Accepted. Well?”

  “Let the protectors die off a quarter of a million years ago. Give the breeders a tenth the time it took humans to evolve on Earth. A tenth of the time, and a lot of nice gaps in the ecology because the protectors didn’t bring anything to prey on the breeders, and a base population in the trillions.

  “See? On Earth there were maybe half a million breeders when the protectors died out. On the Ringworld, three million times the room, and plenty of time to spread out before the protectors died. The mutants would have it all their own way.”

  “I don’t accept that you’re right,” Chmeee said quietly. “I do feel that you’ve missed a point. Granted that the protectors are almost certainly gone. Almost certainly. What if the Hindmost learns that this was their property, their home?”

  “Oops. He’d run. With or without us.”

  “Officially we have not penetrated the secret of the Ringworld’s construction. Agreed?”

  “Yeah.”

  “Are we still looking for the Repair Center? The smell of tree-of-life might be deadly to you. You are too old to become a protector.”

  “I wouldn’t want to. Is there a spectroscope in the lander?”

  “Yes.”

  “Tree-of-life doesn’t grow right without a soil additive: thallium oxide. Thallium must be more common in the galactic core than it is out here. Wherever the protectors spent a lot of their time, we’ll find thallium oxide for the plants. That’s how we’ll find the repair center. We’ll go in in pressure suits, if we ever get that far.”

  Chapter 14 -

  The Scent of Death

  The Hindmost’s voice exploded at them as they reached the road. “... LANDER! CHMEEE, LOUIS, WHAT ARE YOU HIDING? HINDMOST CALLING THE LAND—“

  “Stop! Tanj dammit, turn down the volume, you’ll blow our ears out!”

  “Can you still hear me?”

  “We can hear you fine,” said Louis. Chmeee’s ears had folded into pockets of fur. Louis was wishing he could do that. “The mountains must have blocked us.”

  “And what was it you discussed while we were cut off?”

  “Mutiny. We decided against it.”

  A momentary pause; then “Very wise,” said the Hindmost. “I want your interpretation of this hologram.”

  One of the screens showed a kind of bracket poking out from the rim wall. The picture was slightly blurred, and oddly lit: taken in vacuum, in sunlight and light reflected from the Ringworld landscape on the right. The bracket seemed to be of a piece with the rim wall itself, as if scrith had been stretched like taffy. The bracket held a pair of washers or doughnuts separated by their own diameter. Nothing else showed save the top of the rim wall. It was impossible to guess the scale.

  “This was taken from the probe,” the puppeteer said. “I have inserted the probe into the rim transport system, as advised. It is accelerating to antispinward.”

  “Yeah. What do you think, Chmeee?”

  “It might be a Ringworld attitude jet. It would not be firing yet.”
>
  “Maybe. There are a lot of ways to design a Bussard ramjet. Hindmost, do you get anything in the way of magnetic effects?”

  “No, Louis, the machine seems dormant.”

  “The superconductor plague wouldn’t have touched it in vacuum. It doesn’t look damaged. The controls could be somewhere else, though. On the surface. Maybe they can be repaired.”

  “You would have to find them first. In the Repair Center?”

  “Yeah.”

  The road ran between swampland and stony highlands. They passed what looked like another chemical plant. They must have been seen; there was a deep-throated foghorn sound and a blast of steam from what might have been a chimney. Chmeee didn’t slow down.

  They saw no more of the boxy vehicles.

  Louis had seen pale glimmers passing slowly among the trees, far into the swamp. They moved as slowly as mist on water, or as ocean liners docking. Now, far ahead, a white shape moved free of the trees and toward the road.

  From a vast white bulk the beast’s sense-cluster rose on a slender neck. Its jaw was at ground level; it dropped like a shovel blade, scooping up swamp water and vegetation as the beast cruised uphill on rippling belly muscles. It was bigger than the biggest dinosaur.

  “Bandersnatch,” Louis said. What were they doing here? Bandersnatchi were native to Jinx. “Slow down, Chmeee, it wants to talk to us.”

  “What of it?”

  “They’ve got long memories.”

  “What would they remember? Swamp dwellers, muck-eaters, without hands to make weapons. No.”

  “Why not? Maybe they could tell us what bandersnatchi are doing on the Ringworld in the first place.”

  “That is no mystery. The protectors must have stocked their maps in the Great Ocean with samples of the species they considered potentially dangerous.”

  Chmeee was playing dominance games, and Louis didn’t like it. “What’s the matter with you? We could at least ask!”

  The bandersnatch dwindled behind them. Chmeee snarled, “You avoid confrontation like a Pierson’s puppeteer. Questioning muck-eaters and savages! Killing sunflowers! The Hindmost brought us to this doomed structure against our wills, and you delay our vengeance to kill sunflowers. Will it matter to the Ringworld natives a year from now that Louis the God paused in his passing to pull weeds?”

  “I’d save them if I could.”

  “We can do nothing. It is the road builders we want. Too primitive to threaten us, advanced enough to know answers to questions. We will find an isolated vehicle and swoop down on it.”

  In midafternoon Louis took over the flying.

  The swamp became a river that arched away to spinward, wide of its original bed. The crude road followed the new river. The original bed ran more nearly to port, in careful S-curves, with an occasional stretch of rapids or waterfall. It was dry as bone, running into bone-dry desert. The swamp must have been a sea before it silted up.

  Louis dithered, then followed the original bed.

  “I think we’ve got the timing right,” he told Chmeee. “Prill’s people evolved long after the engineers were gone. Of all the intelligent races here, they were the most ambitious. They built the big, grand cities. Then that odd plague knocked out most of their machinery. Now we’ve got the Machine People, and they could be the same species. The Machine People built the road. They did it after the swamp formed. But I think the swamp formed after Prill’s people’s empire collapsed.

  “So what I’m doing is looking for an old Prill People city. We could get lucky and find an old library or a map room.”

  They had found cities scarce during the first expedition. Today they traveled for some hours without seeing anything except, twice, a cluster of tents, and once, a sandstorm the size of a continent.

  The floating city was still ahead of them, edge on, hiding detail. A score of towers reared around the edge; inverted towers dropped from nearer the center.

  The dry river ended in a dry sea. Louis cruised along the shore, twenty miles up. The sea bed was strange. It was quite flat, except where artfully spaced islands with fluted edges rose from the bottom.

  Chmeee called, “Louis! Set us on autopilot!”

  “What have you found?”

  “A dredge.”

  Louis joined Chmeee at the telescope.

  He had taken it for part of one of the bigger islands. It was huge and flat, disc-shaped, the color of seabottom mud. Its top would have been below sea level. Its seamless rim was angled like the blade of a wood planer. The machine had stalled up against the island it had dredged from the sea bottom.

  So this was how the Ringworld engineers had kept the sludge flowing into the spillpipes. It wouldn’t flow of itself; the sea bottoms were too shallow. “The pipe blocked,” Louis speculated. “The dredge kept going till it broke down, or till something cut the power—something like the superconductor plague. Shall I call the Hindmost?”

  “Yes. Keep him satisfied ...”

  But the Hindmost had bigger news.

  “Observe,” he said. He ran a quick succession of holograms on one of the screens. A bracket poked up and out from the rim wall, with a pair of toroids mounted at its tip. Another bracket, seen from farther away; and in this picture a spill mountain showed at the foot of the rim wall. The spill mountain was half the size of the bracket. A third bracket showed. A fourth, with structures next to it. A fifth—“Hold it!” Louis cried. “Go back!”

  The fifth bracket stayed on the screen for a moment. Its tip held nothing at all. Then the Hindmost flipped back to the fourth hologram.

  It was somewhat blurred by the probe’s velocity. There was heavy lifting machinery anchored to the rim wall next to the bracket: a crude fusion generator; a powered winch; a drum and a hook floating unsupported below it. The cable depending from the drum must be invisibly thin, Louis thought. It could be shadow square wire.

  “A repair team already at work? Uurrr. Are they mounting attitude jets or dismounting them? How many are mounted?”

  “The probe will tell us,” the Hindmost said. “I direct your attention to another problem. Recall to your mind those toroids that circle the waist of the one intact Ringworld spacecraft. We surmise that they generate the electromagnetic scoop fields for Bussard ramjets.”

  Chmeee studied the screen. “The Ringworld ships were all of the same design. I wondered why. You may be right.”

  Louis said, “I don’t understand. What has—“

  Two one-eyed snakes looked out of a screen at him. “Halrloprillalar’s species built part of a transportation system that would give them endless room to colonize and explore. Why didn’t they continue? All of the Ringworld was theirs through the rim transport system. Why would they make the effort to reach the stars?”

  It made an ugly pattern. Louis didn’t want to believe it, but it fit too well. “They got the motors for free. They dismounted a few of the Ringworld attitude jets, built ships around them, and reached the stars. And nothing went obviously wrong. So they dismounted a few more. I wonder how many they used.”

  “The probe will tell us in time,” the puppeteer said. “They seem to have left a few motors still mounted. Why did they not move the Ringworld back into position before the instability grew so great? Chmeee’s question is a good one. Are motors being remounted, or stolen to be used in ships so that a few more of Halrloprillalar’s race may escape?”

  Louis’s laugh was bitter. “How does this sound? They left a few jets in place. Then came a plague that killed off most of their machinery. Some of them panicked. They took all the ships they had, and they built more ships in a hurry and dismounted most of the attitude jets to do it. They’re still at it. They’re leaving the Ringworld to its fate.”

  Chme
ee said, “Fools. They did it to themselves.”

  “Did they? I wonder.”

  “But this is just the possibility I find ominous,” said the puppeteer. “Would they not have taken as much of their civilization as they could move? Certainly they would have taken transmutation machinery.”

  Oddly, Louis was not even tempted to laugh. But what answer could he make?

  The kzin found an answer. “They would take all they could reach. Anything near the spaceport ledges. Anything near the rim wall, where the rim transport system was available. We must search inward, and we must search out the Repair Center. Any of Prill’s people found there would have been trying to save the Ringworld, not leave it.”

  “Perhaps.”

  Louis said, “It would help if we knew just when the plague started eating their superconductors.”

  If he thought the Hindmost would flinch, he was wrong. The puppeteer said, “You will likely learn that before I do.”

  “I think you know already.”

  “Call me if you learn anything.” The snaky heads disappeared.

  Chmeee was looking at him strangely, but he said nothing. Louis returned to the flight controls.

  The terminator line was a vast shadow encroaching from spinward when Chmeee spotted the city. They had followed a sand-filled riverbed to port of the dry sea. The river forked here, and the city nestled in the fork.

  Prill’s people had built tall, even where there was no obvious need. The city had not been wide, but it had been tall, until floating buildings smashed down into the lesser structures below. One slender tower still stood, but at a slant. It had driven itself like a spear into the lower levels. A road ran from port, along the outer edge of one branch of the dry river, then across a bridge so massively braced that it had to belong to the Machine People. Halrloprillalar’s people would have used stronger materials or would have floated it.

  Chmeee said, “The city will have been looted.”

  “Well, yes, given that someone built a road to do the looting. Why don’t you take us down anyway?”