A richly told story of the collision between natureâ€™s smallest organism and historyâ€™s mightiest empire The Emperor Justinian reunified Romeâ€™s fractured empire by defeating the Goths and Vandals who had separated Italy, Spain, and North Africa from imperial rule. In his capital at Constantinople he built the worldâ€™s most beautiful building, married its most powerful empress, and wrote its most enduring legal code, seemingly restoring Romeâ€™s fortunes for the next five hundred years. Then, in the summer of 542, he encountered a flea. The ensuing outbreak of bubonic plague killed five thousand people a day in Constantinople and nearly killed Justinian himself. In Justinianâ€™s Flea, William Rosen tells the story of historyâ€™s first pandemicâ€”a plague seven centuries before the Black Death that killed tens of millions, devastated the empires of Persia and Rome, left a path of victims from Ireland to Iraq, and opened the way for the armies of Islam. Weaving together evolutionary microbiology, economics, military strategy, ecology, and ancient and modern medicine, Rosen offers a sweeping narrative of one of the great hinge moments in history, one that will appeal to readers of John Kellyâ€™s The Great Mortality, John Barryâ€™s The Great Influenza, and Jared Diamondâ€™s Collapse.