The Mediterranean has a habit of keeping secrets. For centuries, historians argued over whether the Roman city of Neapolis in present-day Tunisia truly vanished in a catastrophic event—or whether that story grew taller in the retelling. Now, archaeologists have uncovered sprawling underwater ruins that suggest the legend wasn’t exaggerating after all. Beneath the waves off the coast near modern Nabeul lies what appears to be a massive slice of the ancient city—streets, structures, and industrial installations included—quietly resting on the seabed.