The river was widening now: ever and again it opened into small lakes, upon which tiny islands lay at anchor. There were insects here, brilliantly colored creatures swinging aimlessly to and fro over the surface of the water. Once, despite Theon's shouts, Krif darted away to join his distant cousins. He disappeared instantly in a cloud of glittering wings, and the sound of angry buzzing floated toward them. A moment later the cloud erupted and Krif came back across the water, almost too quickly for the eye to follow. Thereafter he kept very close to Theon and did not stray again.

             Toward evening they caught occasional glimpses of the mountains ahead. The river that had been so faithful a guide was flowing sluggishly now, as if it too were nearing the end of its journey. But it was clear that they could not reach the mountains by nightfall: well before sunset the forest had become so dark that further progress was impossible. The great trees lay in pools of shadow, and a cold wind was sweeping through the leaves. Alvin and Theon settled down for the night beside a giant redwood whose topmost branches were still ablaze with sunlight.

             When at last the hidden sun went down, the light still lingered on the dancing waters. The two boys lay in the gathering gloom, watching the river and thinking of all that they had seen. As Alvin fell asleep, he found himself wondering who last had come this way, and how long since.

             The sun was high when they left the forest and stood at last before the mountain walls of Lys. Ahead of them the ground rose steeply to the sky in waves of barren rock. Here the river came to an end as spectacular as its beginning, for the ground opened in its path and it sank roaring from sight.

             For a moment Theon stood looking at the whirlpool and the broken land beyond. Then he pointed to a gap in the hills.

             "Shalmirane lies in that direction," he said confidently. Alvin looked at him in surprise.

             "You told me you'd never been here before!"

             "I haven't."

             "Then how do you know the way?"

             Theon looked puzzled.

             "I don't know—I've never thought about it before. It must be a kind of instinct, for wherever we go in Lys we always know our way about."

             Alvin found this very difficult to believe, and followed Theon with considerable skepticism. They were soon through the gap in the hills, and ahead of them now was a curious plateau with gently sloping sides. After a moment's hesitation, Theon started to climb. Alvin followed, full of doubts, and as he climbed he began to compose a little speech. If the journey proved in vain, Theon would know exactly what he thought of his unerring instinct.

             As they approached the summit, the nature of the ground altered abruptly. The lower slopes had consisted of porous, volcanic stone, piled here and there in great mounds of slag. Now the surface turned suddenly to hard sheets of glass, smooth and treacherous, as if the rock had once run in molten rivers down the mountain. The rim of the plateau was almost at their feet. Theon reached it first, and a few seconds later Alvin overtook him and stood speechless at his side. For they stood on the edge, not of the plateau they had expected, but of a giant bowl half a mile deep and three miles in diameter. Ahead of them the ground plunged steeply downward, slowly leveling out at the bottom of the valley and rising again, more and more steeply, to the opposite rim. And although it now lay in the full glare of the sun, the whole of that great depression was ebon black. What material formed the crater the boys could not even guess, but it was black as the rock of a world that had never known a sun. Nor was that all, for lying beneath their feet and ringing the entire crater was a seamless band of metal, some hundred feet wide, tarnished by immeasurable age but still showing no slightest trace of corrosion.

             As their eyes grew accustomed to the unearthly scene, Alvin and Theon realized that the blackness of the bowl was not as absolute as they had thought. Here and there, so fugitive that they could only see them indirectly, tiny explosions of light were flickering in the ebon walls. They came at random, vanishing as soon as they were born, like the reflections of stars on a broken sea.

             "It's wonderful!" gasped Alvin. "But what is it?"

             "It looks hke a reflector of some kind."

             "I can't imagine that black stuff reflecting anything."

             "It's only black to our eyes, remember. We don't know what radiations they used."

             "But surely there's more than this! Where is the fortress?"

             Theon pointed to the level floor of the crater, where lay what Alvin had taken to be a pile of jumbled stones. As he looked again, he could make out an almost obliterated plan behind the grouping of the great blocks. Yes, there lay the ruins of once mighty buildings, overthrown by time.

             For the first few hundred yards the walls were too smooth and steep for the boys to stand upright, but after a little while they reached the gentler slopes and could walk without difficulty. Near the bottom of the crater the smooth ebony of its surface ended in a thin layer of soil, which the winds of Lys must have brought here through the ages.

             A quarter of a mile away, titanic blocks of stone were piled one upon the other, like the discarded toys of an infant giant. Here, a section of a massive wall was still recognizable: there, two carven obelisks marked what had once been a mighty entrance. Everywhere grew mosses and creeping plants, and tiny stunted trees. Even the wind was hushed.

             So Alvin and Theon came to the ruins of Shalmirane. Against those walls, if legend spoke the truth, forces that could shatter a world to dust had flamed and thundered and been utterly defeated. Once these peaceful skies had blazed with fires torn from the hearts of suns, and the mountains of Lys must have quailed like living things beneath the fury of their masters.

             No one had ever captured Shalmirane. But now the fortress, the impregnable fortress, had fallen at last—captured and destroyed by the patient tendrils of the ivy and the generations of blindly burrowing worms.

             Overawed by its majesty, the two boys walked in silence toward the colossal wreck. They passed into the shadow of a broken wall, and entered a canyon where the mountains of stone had split asunder.

             Before them lay a great amphitheater, crossed and crisscrossed with long mounds of rubble that must mark the graves of buried machines. Once the whole of this tremendous space had been vaulted, but the roof had long since collapsed. Yet life must still exist somewhere among the desolation, and Alvin realized that even this ruin might be no more than superficial. The greater part of the fortress would be far underground, beyond the reach of Time.

             "We'll have to turn back by noon," said Theon, "so we mustn't stay too long. It would be quicker if we separated. I'll take the eastern half and you can explore this side. Shout if you find anything interesting—but don't get too far away."

             So they separated, and Alvin began to climb over the rubble, skirting the larger mounds of stone. Near the center of the arena he came suddenly upon a small circular clearing, thirty or forty feet in diameter. It had been covered with weeds, but they were now blackened and charred by tremendous heat, so that they crumbled to ashes at his approach. At the center of the clearing stood a tripod supporting a polished metal bowl, not unlike a model of Shalmirane itself. It was capable of movement in altitude and azimuth, and a spiral of some transparent substance was supported at its center. Beneath the reflector was welded a black box from which a thin cable wandered away across the ground.