The invisible ship darted forward. They sped past the barrier of low hills, and were again high above a broad plain. With a startled gasp, Arcot cut their speed. There, floating high in the air, above a magnificent city, was a machine such as no man had ever before seen! It was a titanic airplane--monstrous, gargantuan, and every other word that denoted immensity. Fully three-quarters of a mile the huge metal wings stretched out in the dull light of the cloudy Venerian day; a machine that seemed to dwarf even the vast city beneath it. The roar of its mighty propellers was a rumbling thunder to the men in the _Solarite_. From it came the flashing bursts of flame. On closer inspection, the watchers saw what seemed to be a swarm of tiny gnats flying about the mighty plane. They appeared to be attacking the giant as vainly as gnats might attack an eagle, for they could not damage the giant machine. The flashing bombs burst in blasts of yellow flame as harmlessly as so many firecrackers. All that mighty plane was covered with heavy metal plates, fully ten inches thick, and of metal so tough that when the powerful bombs hit it they made no impression, though they blasted tremendous craters in the soil below. From it poured a steady stream of bombs that burst with a great flash of heat and light, and in an instant the tiny planes they struck streaked down as incandescent masses of metal. Yet the giant seemed unable to approach the city--or was it defending it? No, for it was from the city that the vainly courageous little ships poured out. But certainly it was not these ships that kept the titanic battleship of the air at bay! Tensely the men watched the uneven conflict. The rain of bombs continued, though all fell short of the city. But slowly around the metropolis there appeared an area of flaring, molten lava, and steadily this moved toward the beautiful buildings. Suddenly the battleship turned toward the city and made a short dash inward on its circling path. As though awaiting this maneuver, a battery of hissing, flaming swords of white light flashed upward, a few hundred feet from the ring of molten rock. As the titanic plane rolled, side-slipped out of the way, they passed, harmlessly, barely missing a monstrous wing. "Which?" Arcot demanded. "I say the city. No one should destroy anything so magnificent." Not a dissenting voice was raised, so Arcot sent the _Solarite_ nearer. "But what in the world can we do to that huge thing?" Fuller's voice came eerily out of the emptiness. "It has perfect invulnerability through size alone."