It was not difficult. The necessary knowledge was already in their minds, implanted at birth. The significance lay in the fact that, for the first time in their existence, the robots had acted upon their own initiative, had begun to serve again. Thus the pain ceased. When the pile was finished, the robots felt the return of the pain and, having once begun, they continued to attempt to serve. A great many examined the Factory, found that they were able to improve upon the structure of their bodies, so that they might be better able to serve the Makers when they returned. Accordingly, they worked in the Factory, perfecting themselves--although they could not improve the brains--and many others left the Factory and began to examine mathematics and the physical universe. It was not hard for them to build a primitive spaceship, for the Makers had been on the verge of interstellar flight, and they flew it hopefully throughout the solar system, looking to see if the Makers were there. Finding no one, they left the buildings on Tyban IV as a wistful monument, with a hope that the Makers would some day pass this way and be able to use them. Millenia passed. The pile broke down again, was rebuilt, and so the cycle was repeated. By infinitesimal steps, the robots learned and recorded their learning in the minds of new robots. Eventually they reached the limits of their capability. The pain returned and never left. * * * * * Steffens left his desk, went over and leaned against the screen. For a long while he stood gazing through the mists of carbon air at the pitiful, loyal mechanicals who thronged outside the ship. He felt an almost overwhelming desire to break something, anything, but all he could do was swear to himself. Ball came back, looked at Steffens' eyes and into them. His own were sick. "Twenty-five thousand years," he said thickly, "that's how long it was. _Twenty-five thousand years...._" Steffens was pale and wordless. The mass of the robots outside stood immobile, ageless among rock which was the same, hurting, hurting. A fragment of an old poem came across Steffens' mind. "They also serve who only stand and wait...." Not since he was very young had he been so deeply moved. He stood up rigidly and began to talk to himself, saying in his mind: _It is all over now. To hell with what is past. We will take them away from this place and let them serve and, by God...._ He faltered. But the knowledge of what could be done strengthened him. Earthmen would have to come in ships to take the robots away. It would be a little while, but after all those years a little while was nothing, less than nothing. He stood there thinking of the things the robots could do, of how, in the Mapping Command alone, they would be invaluable. Temperature and atmosphere meant nothing to them. They could land on almost any world, could mine and build and develop.... And so it would be ended. The robots would serve Man.