“Upon learning to read while enslaved, Frederick Douglass began his great journey of emancipation, as such journeys always begin, in the mind. Defying unjust laws, he read in secret, empowered by the wisdom of contemporaries and classics alike to think as a free man. Douglass risked mockery, abuse, beating and even death to study the likes of Socrates, Cato and Cicero. Long after Douglass’s encounters with these ancient thinkers, the Rev. Martin Luther King Jr. would be similarly galvanized by his reading in the classics as a young seminarian — he mentions Socrates three times in his 1963 “Letter From...