 Climate change has been around forever, so the Earth goes through cycles where it gets a little hotter, a little cooler, a little drier, a little wetter. And in those wetter times, in those cooler times, they're able to expand their civilizations. When it's drier and hotter, they return to semi-nomadic ways of life, usually. Basically to go find the water. Exactly, yeah, because they're not getting it. And if you look how massive this wall is, Jim, imagine on top of that you've got a mud brick superstructure.