Dating by the radiocarbon method was useless. Some of the carbon compounds in the various artifacts showed a faint trace of radiocarbon, others showed none. But since the method depends on a knowledge of the amount of nitrogen in the atmosphere of the planet of origin, the rate of bombardment of that atmosphere by high-velocity particles, and several other factors, the information on the radioactivity of the specimens meant nothing. There was also the likelihood that the carbon in the various polymer resins came from oil or coal, and fossil carbon is useless for radio-dating. Nor did any of the more modern methods show any greater success. It had taken Man centuries of careful comparison and cross-checking to read the evolutionary history written in the depths of his own planet's crust--to try to date the city was impossible. It was like trying to guess the time by looking at a faceless clock with no hands. There the city stood--a hundred miles across, ten thousand square miles of complex enigma. It had given Man his first step into the ever-widening field of Cultural Xenology. Dave Turnbull finished his sherry, got up from the breakfast nook, and walked into the living room, where his reference books were shelved. The copy of Kleistmeistenoppolous' "City of Centaurus" hadn't been opened in years, but he took it down and flipped it open to within three pages of the section he was looking for. "It is obvious, therefore, that every one of the indicators points in the same direction. The City was not--_could not have been_--self-supporting. There is no source of organic material on the planet great enough to support such a city; therefore, foodstuffs must have been imported. On the other hand, it is necessary to postulate _some_ reason for establishing a city on an otherwise barren planet and populating it with an estimated six hundred thousand individuals. "There can be only one answer: The race that built the City did so for the same reason that human beings built such megalopolises as New York, Los Angeles, Tokyo, and London--because it was a focal point for important trade routes. Only such trade routes could support such a city; only such trade routes give reason for the City's very existence. "And when those trade routes changed or were supplanted by others in the course of time, the reason for the City's existence vanished." Turnbull closed the book and shoved it back into place. Certainly the theory made sense, and had for a century. Had Duckworth come across information that would seem to smash that theory? The planet itself seemed to be perfectly constructed for a gigantic landing field for interstellar ships. It was almost flat, and if the transhipping between the interstellar vessels had been done by air, there would be no need to build a hard surface for the field. And there were other indications. Every fact that had come to light in the ensuing century had been in support of the Greek-German xenologist's theory.