in the first century A.D., the vital sector in the north—where the realm’s border rested on the Danube and Rhine—had been vulnerable. Above these great rivers the forests swarmed with barbaric Germanic tribes, some of them tamer than others but all envious of the empire’s prosperity. For centuries they had been intimidated by the imperial legions confronting them on the far banks. Now they no longer were. They had panicked, stampeded by an even more fearsome enemy in their rear: feral packs of mounted Hsiung-nu, or Huns.
