Cacio e pepe — cheese and pepper — is the oldest continuously prepared dish in Rome, and possibly the simplest great dish in the world. Its origin is with the transhumance shepherds of the Apennine mountains, who drove their flocks between the summer pastures of the high mountains and the winter grazing of the Roman campagna along ancient droving roads called tratturi. They carried three things in their packs: dried pasta, aged Pecorino from their own flocks' milk, and black peppercorns from the spice merchants of Rome's Testaccio market.
The pepper served a practical function beyond flavor: in the days before refrigeration, the shepherd ate in the open air where temperatures at altitude could drop sharply at night, and the thermogenic properties of black pepper — its ability to raise the body's core temperature slightly — were understood empirically by people who had been eating it for generations. The Pecorino provided the fat and protein that sustained a full day's walking. The pasta provided the carbohydrate. Together, they produced a complete system of nutrition from three ingredients.
The bean adaptation — substituting cannellini beans for pasta, adding broth to create a silky, soup-adjacent texture — is a Roman innovation of the postwar period, emerging from the cucina povera tradition that sought to extend the flavors of the great dishes to ingredients that were cheaper and more available. The result is arguably superior to the original: the beans carry the Pecorino and pepper with more structural interest than pasta, and the broth makes the dish feel simultaneously lighter and more sustaining. The shepherd would have approved.