Guardian of the North: A colossal metal column that uses the power of magnetism to attract then destroy fliers that attempt to enter Okar, the land of the yellow Martians.
“I turned my eyes once more toward the flier. She was moving rapidly toward the city, and when she had come close enough I was surprised to see that her propellers were idle. Straight for that grim shaft she bore. At the last minute I saw the great blades move to reverse her, yet on she came as though drawn by some mighty, irresistible power.
I"ntense excitement prevailed upon her deck, where men were running hither and thither, manning the guns and preparing to launch the small, one-man fliers, a fleet of which is part of the equipment of every Martian war vessel. Closer and closer to the black shaft the ship sped. In another instant she must strike, and then I saw the familiar signal flown that sends the lesser boats in a great flock from the deck of the mother ship. Instantly a hundred tiny fliers rose from her deck, like a swarm of huge dragon flies; but scarcely were they clear of the battleship than the nose of each turned toward the shaft, and they, too, rushed on at frightful speed toward the same now seemingly inevitable end that menaced the larger vessel.
"A moment later the collision came. Men were hurled in every direction from the ship's deck, while she, bent and crumpled, took the last, long plunge to the scrap-heap at the shaft's base. With her fell a shower of her own tiny fliers, for each of them had come in violent collision with the solid shaft. I noticed that the wrecked fliers scraped down the shaft's side, and that their fall was not as rapid as might have been expected; and then suddenly the secret of the shaft burst upon me, and with it an explanation of the cause that prevented a flier that passed too far across the ice-barrier ever returning.
"The shaft was a mighty magnet, and when once a vessel came within the radius of its powerful attraction for the aluminum steel that enters so largely into the construction of all Barsoomian craft, no power on earth could prevent such an end as we had just witnessed. I afterward learned that the shaft rests directly over the magnetic pole of Mars, but whether this adds in any way to its incalculable power of attraction I do not know. I am a fighting man, not a scientist. . .
"The moment that the last of the fliers came to rest at the base of the shaft the black-bearded, yellow warriors swarmed over the mass of wreckage upon which they lay, making prisoners of those who were uninjured and occasionally dispatching with a sword-thrust one of the wounded who seemed prone to resent their taunts and insults. A few of the uninjured red men battled bravely against their cruel foes, but for the most part they seemed too overwhelmed by the horror of the catastrophe that had befallen them to do more than submit supinely to the golden chains with which they were manacled.”