"It depends," Ashe remarked, "upon the type of civilization. The Egyptians built in stone, grandly. They used tools and weapons of copper, bronze, and stone, and they were considerate enough to operate in a dry climate which preserved relics well. The cities of the Fertile Crescent built in mud brick and used stone, copper, and bronze tools. They also chose a portion of the world where climate was a factor in keeping their memory green. "The Greeks built in stone, wrote their books, kept their history to bequeath it to their successors, and so did the Romans. And on this side of the ocean the Incas, the Mayas, the unknown races before them, and the Aztecs of Mexico all built in stone and worked in metal. And stone and metal survive. But what if there had been an early people who used plastics and brittle alloys, who had no desire to build permanent buildings, whose tools and artifacts were meant to wear out quickly, perhaps for economic reasons? What would they leave us--considering, perhaps, that an ice age had intervened between their time and ours, with glaciers to grind into dust what little they did possess? "There is evidence that the poles of our world have changed and that this northern region was once close to being tropical. Any catastrophe violent enough to bring about a switch in the poles of this planet might well have wiped out all traces of a civilization, no matter how superior. We have good reason to believe that such a people must have existed, but we must find them. "And Ashe is a convert from the skeptics--" the major slipped down from his perch on the wall shelf--"he is an archaeologist, one of your tomb discoverers, and knows what he is talking about. We must do our hunting in time earlier than the first pyramid, earlier than the first group of farmers who settled by the Tigris River. But we have to let the enemy guide us to it. That's where you come in." "Why me?" "That is a question to which our psychologists are still trying to find the answer, my young friend. It seems that the majority of the people of the several nations linked together in this project have become too civilized. The reactions of most men to given sets of circumstances have become set in regular patterns and they cannot break that conditioning, or if personal danger forces them to change those patterns, they are afterward so adrift they cannot function at their highest potential. Teach a man to kill, as in war, and then you have to recondition him later. "But during these same wars we also develop another type. He is the born commando, the secret agent, the expendable man who lives on action. There are not many of this kind, and they are potent weapons. In peacetime that particular collection of emotions, nerve, and skills becomes a menace to the very society he has fought to preserve during a war. He is pressured by the peaceful environment into becoming a criminal or a misfit.