At his peak, Desiderius Erasmus accounted for up to a fifth of all book sales across a continent, yet he began life in the late 1460s as the illegitimate child of a Catholic priest, orphaned by plague in 1483, cheated of his inheritance, and forced by poverty into permanent vows at an Augustinian canonry. This episode traces how his mastery of Latin became his ticket out, first as secretary to the Bishop of Cambrai and then to Paris and England, where he found intellectual equals in Thomas More and John Colet before losing every coin he owned to English customs officials.

We explore his principle of ad fontes, back to the sources, his satirical bestseller The Praise of Folly, his philosophy of Christ in the Enchiridion, and the Greek New Testament that exposed translation errors in the Vulgate, including the shift from do penance to change your mind that undercut the sale of indulgences. The episode then follows him into the Reformation crossfire, his debate with Martin Luther over free will, his refusal to join either side, his flight from Basel in 1529, and his death in 1536, along with the modern legacy of tolerance that bears his name.

• Why his years at Stein forged a lifelong conviction that piety must be voluntary
• How Erasmus used the printing press to popularize complex ideas for a mass audience
• The metanoia translation and why one word threatened the church’s revenue stream
• The Catholic accusation that he laid the egg that Luther hatched
• Whether his principled middle road was cowardice or courage, and what it cost him