William Manchester's A World Lit Only by Fire: The Medieval Mind and the Renaissance investigates the causes of the Dark Ages and the people and events that led to the birth of the Renaissance. The book, published in 1992, is notable for its lively storytelling and portrayals of some of the greatest villains and heroes of the period. A World Lit Only by Fire is intended as an entertaining, informative book about a period in history whose import continues into modern day.

The book is divided into three parts. Part 1, "The Medieval Mind," is a survey of the attitudes and mental states of the common people during the Dark Ages. Manchester is scathing in his portrayal of the ignorance and anti-intellectualism of the time. The "medieval mind" as he describes it was essentially a mind without the capacity to doubt, to form a sense of self, or to aspire to anything beyond the day’s toil. Christian missionaries were spreading the gospel wherever they could, finding particular success among the pagan tribes. The Catholic Church ostensibly provided answers to all of life’s most important questions and its decrees were unassailable. Many of the new converts failed to abandon their old faiths and instead assimilated them into their new status as Christians.

Part 2, "The Shattering," discusses the events that led to the end of both the Dark Ages and what Manchester refers to as the "medieval mind." Much of the section is spent highlighting the various corruptions and excesses of the Catholic Church and its leaders. He uses a colorful cast of violent, lewd, and cunning characters as his examples, including various Popes, the notorious Borgia family, Niccolò Machiavelli, Erasmus, John Calvin, Leonardo da Vinci, Martin Luther, Johannes Gutenberg, Sir Thomas More, and many others. Martin Luther receives the most attention in "The Shattering," as it was his public criticisms of the Church that led to the religious reformation that would eventually lead to the decentralization of the Church’s power. In the wake of Luther’s reform, new Christian branches sprouted and began to fight each other with all of the aggression and intolerance they had ever used against the Vatican. At the end of Part 2, the stage has been set for the birth of the Renaissance and the conclusion of the Dark Ages.

Part 3, "One Man Alone," traces the most famous voyages of the Portuguese explorer Ferdinand Magellan, who Manchester frames as the hero of the book. Magellan’s daring, dangerous trip would lead to the first circumnavigation of the globe, proving inarguably that the earth is a sphere. The conviction that the earth was flat was one of the last pillars upon which the medieval mind rested. Magellan would eventually be killed in a battle in the Philippines, as a result of trying to convert the natives to Christianity, but Manchester cites his achievements as outranking nearly anyone else’s in terms of bringing an end to the primitive mindset that preceded The Renaissance.