Plato is one of history's most influential thinkers, yet the image we have of him—an ethereal figure far removed from society and politics, who conjured abstract ideas in peaceful groves—is a fiction, created by Plato's admirers and built up over centuries.

In Plato and the Tyrant, acclaimed historian and classicist James Romm draws on personal letters of Plato to show how a philosopher helped topple the leading Greek power of the era: the opulent city of Syracuse. There, Plato encountered two authoritarian rulers, a father and son both named Dionysius, and tried to steer them toward philosophy. At the same time, he worked on his masterpiece, Republic, in which he conceived a ruler who unites perfect wisdom with absolute power. That dream has echoed down through the ages and given rise to a famous term, one that Plato himself didn't actually use: philosopher-king. As Romm reveals, Plato's time in Syracuse helped shape Republic—and also had disastrous results for Plato himself and for all of Greek Sicily. The younger Dionysius welcomed Plato with open arms, but soon the relationship soured. Plato's close friendship with Dionysius's uncle, Dion—possibly a bond of romantic love—created a rift in the ruling family that led to a chaotic civil war. Plato and the Tyrant demonstrates how Plato's experiment with enlightened autocracy spiraled into catastrophe.