TIL I learned of the "Tartarian Empire" conspiracy theory, which holds that all those large 19th century buildings were actually built by a prior global civilization that was destroyed by "mud floods"

I mean, how do you deal with something like that? There were so many buildings of that type because cities in the 19th century were growing rapidly thanks to growing populations and industrialization, and European Colonialism exported this kind of building style to the rest of the world. This is no great mystery, and there is ample documentary evidence for this.

I wish I could believe that the adherents of this notion did so as a joke. But alas, here we are...