History is rife with lost treasures, from Aztec gold hidden during the Spanish conquest to the Ark of the Covenant, which vanished during the destruction of Jerusalem over 2,500 years ago. In his book, "The Museum of Lost Things: True Tales of Fabled Treasures, Legendary Cities, and Mythical Creatures That Vanished From History" (National Geographic Books, 2026), writer Sam Kean examines all things lost to time. In this excerpt from the book, he looks at how the tomb of Genghis Khan, arguably the most successful ruler in history, has remained hidden for nearly 800 years and counting. If archaeologists could vote on which lost grave they'd most like to find, Genghis Khan's would likely appear...