Beneath the scrublands of northeastern Brazil, 200 million earthen mounds — some standing for 4,000 years — have long been mistaken for termite homes. Researchers have now revealed they are something far stranger: the displaced soil of a subterranean tunnel network spanning an area the size of Great Britain, quietly engineered by a single insect species across millennia. This discovery invites us to reconsider what we mean by civilization, and which creatures on Earth have most durably shaped the ground beneath our feet.