In the year A.D. 9 Varus, a Roman general, marched an army of three legions to the Rhine River in Germany to help protect Rome's eastern border. The legions totaled approximately fifteen thousand infantry and five hundred cavalry. Arminius, a German chieftain, lured Varus's army into a nearby forest (the Teutoburg Forest) where his troops were waiting in ambush. The ensuing battle ended in the total annihilation of all three Roman legions. The defeat of the expertly trained, well-equipped, and highly disciplined Roman military force at the hands of a barbarian army that was almost completely lacking in comparable military expertise was a harbinger. What weighted the battle in favor of the Germans was the enormous number of warriors they brought into the fray, all aimed at the heart of Varus's three legions. Three centuries later, when a seemingly endless procession of German tribes—the...