Aurelian—a gritty Balkan soldier—seized a crumbling Roman Empire in AD 270. His five-year reign still stuns: how did he crush Germanic hordes, topple Zenobia’s Palmyrene Empire and reunite the Gallic Empire under Roman rule? But Aurelian was more than a conqueror. He constructed miles of walls around Rome, and erected a massive temple to Sol Invictus--god of the unconquered sun.