T hey make a desert and call it peace.” So the Roman historian Tacitus, writing at the end of the first century A.D., describes the devastating result of Roman imperial conquest. Tacitus assigns these words to the Briton chieftain Calgacus, who faced the inexorable advance of Roman legions in Britain. When he wrote these words, Tacitus was likely thinking of the devastation inflicted on Gaul 130 years* earlier by Julius Caesar. By any measure, the carnage Caesar’s troops inflicted on Gaul was vast. During the eight-year campaign, Caesar’s armies are estimated to have killed over one million Gauls, the entire population of the city of Rome at its height. Yet this bloodshed, like many mass outpourings of organized violence in human history, laid a foundation for future prosperity and cultural blossoming, and had an undeniably civilizing effect on the known world for centuries to come. From the perspective of a millennium later, another historian of Rome, Edward Gibbon, would write that “if a man were called to fix the period in the history of the world, during which the condition of the human race was most happy and prosperous, he would, without hesitation, name that which elapsed from the death of Domitian to the accession of Commodus,” the very period in which Tacitus lived. The history of Rome and its legacy for the modern world is shot through with this tension between rapacious, violent conquest and the spread of peaceful civilization, the famous Pax Romana