But soon these last representatives of animal life vanished, and three vertical leagues down, the Nautilus passed below the limits of underwater existence just as an air balloon rises above the breathable zones in the sky. We reached a depth of 16,000 meters—four vertical leagues—and by then the Nautilus’s plating was tolerating a pressure of 1,600 atmospheres, in other words, 1,600 kilograms per each square centimeter on its surface!

— Twenty Thousand Leagues Under the Sea (Extraordinary Voyages, #6) by Jules Verne