«I think so,» replied Alvin. «It’s a map of the entire transport system, and those little circles must be the other cities of Earth. I can just see names beside them, but they’re too faint to read.»

«There must have been some form of internal illumination once,» said Khedron absently. He was tracing the lines beneath his feet, following them with his eyes out toward the walls of the chamber.

«I thought so!» he exclaimed suddenly. «Do you see how these radiating lines lead toward the small tunnels?»

Alvin had noticed that besides the great arches of the moving ways there were innumerable smaller tunnels leading out of the chamber-tunnels that sloped downward instead of up.

Kedron continued without waiting for a reply.

It would be hard to think of a simpler system. People would come down the moving ways, select the place they wished to visit, and then follow the appropriate line on the map.

«And what happened to them after that?» asked Alvin. Khedron was silent, his eyes searching out the mystery of those descending tunnels. There were thirty or forty of them, all looking exactly the same. Only the names on the map would have enabled one to distinguish between them, and those names were indecipherable now.

Alvin had wandered away and was circumnavigating the central pillar. Presently his voice came to Khedron, slightly muffled and overlaid with echoes from the walls of the chamber.

«What is it?’ called Khedron, not wishing to move, because he had nearly succeeded in reading one of the dimly visible groups of characters. But Alvin’s voice was insistent, so he went to join him.

Far beneath was the other half of the great map, its faint webwork radiating to the points of the compass. This time, however, not all of it was too dim to be clearly seen, for one of the lines and only one-was brilliantly illuminated. It seemed to have no connection with the rest of the system, and pointed like a gleaming arrow to one of the downward-sloping tunnels. Near its end the line transfixed a circle of golden light, and against that circle was the single word LYS. That was all.

For a long time Alvin and Khedron stood gazing down at that silent symbol. To Khedron it was a challenge he knew he could never accept-and which, indeed, he would rather did not exist. But to Alvin it hinted at the fulfillment of all his dreams; though the word Lys meant nothing to him, he let it roll around his mouth, tasting its sibilance like some exotic flavor. The blood was pounding in his veins, and his cheeks were flushed as by a fever. He stared around this great concourse, trying to imagine it as it had been in the ancient days, when air transport had come to an end but the cities of Earth still had contact with one another. He thought of the countless millions of years that had passed with the traffic steadily dwindling and the lights on the great map dying one by one, until at last only this single line remained. How long, he wondered, had it gleamed there among its darkened companions, waiting to guide the steps that never came, until Yarlan Zey had sealed the moving ways and closed Diaspar against the world?

And that had been a billion years ago. Even then, Lys must have lost touch with Diaspar. It seemed impossible that it could have survived; perhaps, after all, the map meant nothing now.

Khedron broke into his reverie at last. He seemed nervous and ill at ease, not at all like the confident and self-assured person that he had always been in the city above.

«I do not think that we should go any farther now,» he said. «It may not be safe until-until we are more prepared.»

There was wisdom in this, but Alvin recognized the underlying note of fear in Khedron’s voice. Had it not been for that, he might have been sensible, but a too-acute awareness of his own valor, combined with a contempt for Khedron’s timidity, drove Alvin onward. It seemed foolish to have come so far, only to turn back when the goal might be in sight.

«I’m going down that tunnel,» he said stubbornly, as if challenging Khedron to stop him. «I want to see where it leads.» He set off resolutely, and after a moment’s hesitation the Jester followed him along the arrow of light that burned beneath their feet.

As they stepped into the tunnel, they felt the familiar tug of the peristaltic field, and in a moment were being swept effortlessly into the depths. The journey lasted scarcely a minute; when the field released them they were standing at one end of a long narrow chamber in the form of a halfcylinder. At its distant end, two dimly lit tunnels stretched away toward infinity.

Men of almost every civilization that had existed since the Dawn would have found their surroundings completely familiar, yet to Alvin and Khedron this was a glimpse of another world. The purpose of the long, streamlined machine that lay aimed like a projectile at the far tunnel was obvious, but that made it none the less novel. Its upper portion was transparent, and looking through the walls Alvin could see rows of luxuriously appointed seats. There was no sign of any entrance, and the entire machine was floating about a foot above a single metal rod that stretched away into the distance, disappearing in one of the tunnels. A few yards away another rod led to the second tunnel, but no machine floated above it. Alvin knew, as surely as if he had been told, that somewhere beneath unknown, far-off Lys, that second machine was waiting in another such chamber as this.

Khedron began to talk, a little too swiftly.

«What a peculiar transport system! It could only handle a hundred people at a time, so they could not have expected much traffic. And why did they go to all this trouble to bury themselves in the Earth if the skies were still open? Perhaps the Invaders would not even permit them to fly, though I find that hard to believe. Or was this built during the transition period, while men still traveled but did not wish to be reminded of space? They could go from city to city, and never see the sky and the stars.» He gave a nervous laugh. «I feel sure of one thing, Alvin. When Lys existed, it was much like Diaspar. All cities must be essentially the same. No wonder that they were all abandoned in the end, and merged into Diaspar. What was the point of having more than one?»

Alvin scarcely heard him. He was busy examining the long projectile trying to find the entrance. If the machine was controlled by some cental or verbal code order, he might never be able to make it obey him, and it would remain a maddening enigma for the rest of his life.

The silently opening door took him completely unawares. There was no sound, no warning when a section of the wall simply faded from sight and the beautifully designed interior lay open before his eyes.

This was the moment of choice. Until this instant, he had always been able to turn back if he wished. But if he stepped inside that welcoming door, he knew what would happen, though not where it would lead. He would no longer be in control of his own destiny, but would have placed himself in the keeping of unknown forces.

He scarcely hesitated. He was afraid to hold back, being fearful that if he waited too long this moment might never come again-or that if it did, his courage might not match his desire for knowledge. Khedron opened his mouth in anxious protest, but before he could speak, Alvin had stepped through the entrance. He turned to face Khedron, who was standing framed in the barely visible rectangle of the doorway, and for a moment there was a strained silence while each waited for the other to speak.

The decision was made for them. There was a faint flicker of translucence, and the wall of the machine had closed again. Even as Alvin raised his hand in farewell, the long cylinder started to ease itself forward. Before it had entered the tunnel, it was already moving faster than a man could run.