That first day on Mars was all work. We went to the nearest rocket ship that had landed with us, the one that remained upright, and unpacked its cargo. Since this rocket was not going to leave Mars there was much more gear aboard because no extra fuel had been carried. Most valuable of the equipment were two Mars-cars, self-propelled vehicles which were similar to those used in exploring the moon. They were four-wheeled, with a cabin swung in the middle. Each wheel was equipped with tires sixteen feet in diameter. Although the machine itself was almost as large as a freight car, it was constructed of aluminum and lightweight alloys and even on earth it would not weigh as much as an ordinary motorcar. The Mars-cars were electrically driven, powered by specially built storage batteries which could be charged from solar cells built into our main rocket. Also aboard the rocket was ore sampling equipment, which we expected to use in studying the geology of Mars. Dr. Spartan put Warner Joel to work with the digging tools to construct a moat around our headquarters ship. Instead of a drawbridge, a causeway was left to the north of the ship, running diagonally across the moat. Rocks were piled in the middle of the causeway so that two paths were left for the tires of the Mars-cars. A hostile force attempting to cross the causeway could be enfiladed by pistol and rifle fire from behind a small breastworks at the base of the ship, or from the locks of the ship itself. It was while digging this moat that Dr. Joel found rubies. The soil was full of them. They were more plentiful than pebbles on the earth. "Possibly a lot of the color of the Martian sand is due to aluminum oxide tinctured with chromium," Joel explained. He assumed we all knew this was the chemical composition of rubies. "I suspected the Martians used lidar," said Axel. And, of course, he assumed we all knew that lidar was light radar, which physicists on the earth were just learning how to use. It's a method of amplifying light through a special tube of artificial rubies. The light excites the chromium in the rubies and causes the atoms to give off a red glow. The resulting red beam can be focused to pencil thinness and sent vast distances. Scientists believe that some of the nearer stars--meaning stars within the range of ten light years distant from the sun--can be explored by lidar. We had unpacked most of the gear from the two ships and had assembled the Mars-cars by noon the next day. "Ludson," said Spartan, "take Drake over to the No. three ship and bring back all the supplies you can carry. The rest of us will make our living quarters habitable." "Yes, sir," said Axel. He turned to me. "Come on, Bill. Let's get started." "If you see signs of life," Spartan said, "shoot first." "But, sir," Axel protested, "wouldn't it be best for us not to do anything unless we're attacked?"