In a shuttered bedroom in ancient Italy, the sleepless Pliny the Elder lies in bed obsessively dictating new chapters of his Natural History to his slave Diocles. Fat, wheezing, imperious, and prone to nosebleeds, Pliny does not believe in spending his evenings in repose: No—to be awake is to be alive. There’s no time to waste if he is to classify every element of the natural world in a single work. By day Pliny the Elder carries out his many civic duties and gives the occasional disastrous public reading. But despite his astonishing ambition to catalog everything from precious metals to...