For as we shot down toward the great pit of the mighty force-ray we had seen clearly now the scores of giant domed, humped shapes on Triton's roof around that pit, which we had vaguely discerned from high above. And they were, as Whitely cried to us, great forts! Giant domed forts of inconceivably thick and strong metal, each hundreds of feet in height, with openings here and there in them from which countless deadly weapon-rays could be emitted. And these great domed forts, over a hundred in number, were _moving_, were wheeling this way and that smoothly and swiftly on Triton's roof, were circling slowly on that roof about the pit of the giant sun-ray, guarding that pit and the control-boxes in its walls! Even as we heard Whitely's cry in that moment, as we flashed down toward them, we realized that the Neptunians had constructed those mighty moving forts of metal to guard their great force-ray's controls from our attack, placing more than a hundred of them around the pit of the great sun-ray, and a half-score of them, as we had perceived, around the pit of the other great force-ray on Triton's other side! And then, in the moment that Whitely cried out and that we saw those great forts moving like smooth-gliding mountains of metal beneath us, there had rained upward from them toward us a staggering, withering storm of concentrated force-rays! Reeling, staggering, falling, our fleet spun in crazy disorder in the next moment as that terrific fire from beneath decimated us! And though in the next instant Marlin's voice rang steel-clear with an order, though in answer to that order our own concentrated rays radiated down madly toward those gliding mountain-like domed forts beneath us, it seemed that our rays had no effect upon them! For so stupendous in thickness and strength were those giant domed forts of metal, that instead of cleaving through them our rays could do no more than crumple and dent somewhat their smooth outer surfaces! They were invulnerable, almost, to our attack, and though one of them was crumpled into twisted metal by scores of our rays happening to converge upon it, the others were almost unharmed and were raking us with a terrible, annihilating rain of rays as we shot down over them!