We all know it’s good to hydrate. Water can be so blah though. So when I’m trying to rehydrate after a long run in the summer heat, I tend to reach for an old-timey solution: The energy drink of ancient Rome.The Romans were famed for their innovations in military logistics, which allowed them to extend their territory from Rome and its immediate surrounds to the whole Mediterranean and ultimately, with the establishment of the Roman Empire, virtually all of western Eurasia. But an army can’t win if it’s thirsty. Enter posca. This blend of vinegar and water—and possibly salt, herbs, and other stuff—holds a special place in beverage history thanks to its role as the Gatorade of the Roman army.