"In republican times, one of Rome's deadliest enemies was King Mithridates of Pontus. In 66 BCE, after decades of inconclusive struggle, the tribune Manilius proposed a bill that would give supreme command in the war against Mithridates to Pompey the Great, who had just swept the Mediterranean clean of another menace: the pirates. While powerful aristocrats objected to the proposal, which would endow Pompey with unprecedented powers, the bill proved...