The previously untold story of the watershed battle that changed the course of Western history. In AD 9, a Roman traitor led an army of barbarians who trapped and then slaughtered three entire Roman legions: 20,000 men, half the Roman army in Europe. If not for this battle, the Roman Empire would surely have expanded to the Elbe River, and probably eastward into present-day Russia. But after this defeat, the shocked Romans ended all efforts to expand beyond the Rhine, which became the fixed border between Rome and Germania for the next 400 years, and which remains the cultural border between Latin western Europe and Germanic central and eastern Europe today.