While man was learning the rules of space flight, these creatures had been building their first spaceships. Strange contest! Though neither human nor Centaur suspected the existence of the other, each progressed about as rapidly, as if linked by cosmic telepathy. Each race colonized its own system and gradually built up speeds great enough for interstellar travel. Indeed, the first human ship had just left for Centauri when the first vessel of the Centaurs landed on Mars. For a time, it seemed that a beneficial union of two races had been established. Then it was discovered that the aliens had moral standards so different from humans that life with them was impossible. Though small groups of them visiting Earth or the planets were well-behaved and gracious guests, they were likely when they outnumbered their hosts to turn their thoughts to vivisection. Or to casual massacre, if they decided that humans annoyed them. So outraged humanity had declared war, driven the visitors from the system. But at that point the war virtually ended. It was impossible for either Earth or Centauri to send a serious invasion fleet into the other's home system because of the tremendous distance! In either case, the defenders would have an advantage that could not be overcome! * * * * * Lance O'Dea felt perspiration trickling down his face. He studied the happy aliens. Morguma waved his weapon. "You will please to come out, our beloved brothers of Earth! It will create difficulty to remove your ship to a more auspicious location if you do not remove yourselves from it first!" The two men descended from the lock. Above them a Centaur ship hovered, darted out pale green seizure beams. In the grip of the beams, the Earth ship slid back from the mesa edge to more secure ground. Behind Morguma, more Centaurs were coming up, their features masked with broad happy grins. The Centaur leader stepped aside, motioned the men to precede him. Flanked by the armed guards, they marched across the mesa, reached a broad trail that led into a valley below. O'Dea stopped short in surprise. He stared into the broad valley. "Is it not inspiring?" Morguma enthused, behind him. "Our beautiful rocket center that we created on this formerly barren world! Oh it makes my heart sing with joy!" The two men, eyes wide, looked down at the teeming Centaur life that filled the immense valley. Great factories sprawled for miles, apparently engaged in manufacturing and servicing space ships. Thousands of craft were berthed in neat rows for as far as they could see. From small one passenger jobs to deadly battle cruisers they were taking off and landing by the hundreds. "There aren't that many ships in the universe," O'Dea mumbled, dazed. "And millions of Centaurs! Of all the places we could have landed--" He felt a polite prodding in his spine.