10. Cahokia
Near present-day St. Louis, Cahokia was once the largest and most sophisticated city north of Mexico, with towering earthen mounds and a vibrant culture. Around 1350 CE, its population dwindled rapidly and the city was abandoned. Scholars suggest environmental stress—like flooding or resource depletion—as well as political and social upheaval may have triggered the sudden collapse. Today, Cahokia’s mysterious ruins hint at a once-great urban center lost to time. Read more at Smithsonian Magazine.
