For twenty years, the Roman Empire conquered its way through modern-day Germany, claiming all lands from the Rhine to the Elbe. However, when at last all appeared to be under control, a catastrophe erupted that claimed the lives of 10,000 legionnaires and laid Rome's imperial ambitions for Germania into the dust. In late September of 9 AD, three Roman legions, while marching to suppress a distant tribal rebellion, were attacked in a four-day battle with the Germanic barbarians. The Romans, under the leadership of the province's governor, Publius Quinctilius Varus, were taken completely by surprise, betrayed by a member of their own ranks: the German officer and secret rebel leader, Arminius. The defeat was a heavy blow to both Rome's military and its pride. Though the disaster was ruthlessly avenged soon afterwards, later attempts at conquering the Germans were half-hearted at best. Four days in September thoroughly examines the ancient sources and challenges the hypotheses of modern scholars to present a clear picture of the prelude to the battle, the fighting itself and its aftermath.