After they evolve from Grotle, Torterra quickly get used to Sudowoodo impersonating the trees on their back, or Starly nesting in the real trees, and as they grow in size they become home to a wider and wider variety of pokemon. There is no known limit to a Torterra's natural lifespan, but when they reach a sufficiently colossal size they cease to reproduce, become unable to eat, and must survive on photosynthesis. Often, bereft of energy, they go into periods of hibernation which can last for millions of years.
Pioneers have often tried to avoid building their cities on the backs of Torterra, but these pokemon have grown so large and covered in dirt, rock, and vegatation there they are impossible to avoid. Whole cities have been found relocated after a night of the ground shaking and moving beneath them, or dug deep into the ground to be confronted with a telltale white spike or green shell, and travelers have often been knocked over by powerful roars, then watched the Torterra on whose back their destination rested walk briskly away. At times, the Torterra do battle with one another, the world begins to shake, and people fall to their deaths off the rounded sides of its shell or are trampled by a pokemon which dwarf even Wailord in size. Snorlax may block the road, but Torterra are the road, and often the destination as well.
Torterra are adept swimmers and perfectly buoyant, and many a Torterra has been mistaken over the years for an uninhabited island. Yet nothing could have prepared us for the relevation that one of the most terrifying parts of our foundation legend was absolutely true. One can only wonder what will happen to the civilization on its back when the Torterra named Sinnoh awakens once more.
Lyraeon deserves full credit for giving me the idea for this entry and then, after I somehow didn't write it down, remembering it in great detail months later. She has my complete thanks.