That very morning, while Professor Stevens and his party were still exchanging experiences with Captain Petersen and the members of the crew, Von Ullrich sent for them and they gathered with his own men in the small lock-chamber at the base of the pyramid. There they were provided with temporary suits by their host, since their own--which they brought along--could be inflated only from the _Nereid_. Beside her, they noted as they emerged in relays, the U-boat was now moored. Entering their own craft, they got under way at once and headed swiftly westward toward the brink of the plateau. Most of Von Ullrich's crew were with them, though a few had been left behind to guard against any treachery, on the part of the now sullen and aroused populace. Slipping out over the edge of that precipitous tableland, they tilted her rudders and dove to the abysm below. Presently the central square of the illuminated panel in the navigating room showed three great concentric circles, enclosed by a quadrangle that must have been miles on a side--and within this vast sunken fortress lay a city of innumerable pyramids and temples and palaces. The German's eyes flashed greedily as he peered upon this vision. "There you are!" he exclaimed, quivering with excitement. "Those circles, that square: what would you judge they were, Professor?" "I would judge that originally they were the canals bearing the municipal water supply," Martin Stevens told him quietly, suppressing his own excitement, "for such was said to be the construction of the City of the Golden Gates; but now I judge they are walls raised on those original foundations by the frantic populace, when the submergence first began, in a vain effort to hold back the tides that engulfed them." "And do you think they are of gold?" "Frankly, no; though I have no doubt you will find plenty of that element down there." Nor was the prediction wrong, for modern eyes had never seen such a treasure house as they beheld when presently the _Nereid_ came to rest outside that ancient four-walled city and they forced their way inside. * * * * * Though the walls were not of gold, the inner gates were, and the temples were fairly bursting with the precious metal, as well as rare jewels, the eyes of a thousand idols gleaming with rubies and emeralds. But where was the populace, amid all this prodigious wealth? Was there no life down here? Von Ullrich declared through the vibrator of his pressure-suit that he had heard there was. And as though in substantiation, many of the temples showed the same bell-jar construction as the pyramids above, though even stouter, revealing evidences of having been occupied very recently; but all were flooded and empty. The city was as a city of the dead. This ominous sign did not deter the "emperor," however. Ruthlessly he and his men looted those flooded temples, forcing Professor Stevens and his party to lend aid in the orgy of pillage.