Marcus Agrippa personified the term 'right-hand man'. As Emperor Augustus' deputy, he waged wars, pacified provinces, beautified Rome, and played a crucial role in laying the foundations of the Pax Romana for the next two hundred years but he served always in the knowledge he would never rule in his own name. Why he did so, and never grasped power exclusively for himself, has perplexed historians for centuries. In his teens, he formed a life-long...