An alternative-history conspiracy theory has been taking root on YouTube and Reddit forums. It alleges that a long-enduring, advanced society called Tartaria built much of our perennial architecture worldwide. After a catastrophic mudslide took out most Tartarian citizens, the theory goes, their remaining buildings are now being systematically dismantled to suppress the truth about their origin. How much of this theory is true? And why is it gaining traction right now?

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