In the fourth part of the series, Diarmaid MacCulloch makes sense of the Reformation, and of how a faith based on obedience and authority gave birth to one based on individual conscience. He shows how Martin Luther wrote hymns to teach people the message of the Bible, and how a tasty sausage became the rallying cry for Swiss Reformer Ulrich Zwingli to tear down statues of saints, allow married clergy and deny that communion bread and wine were the body and blood of Christ.

Professor Diarmaid MacCulloch - one of the world's leading historians - reveals the origins of Christianity and explores what it means to be a Christian. In the first episode, he overturns the familiar story that it all began when the apostle Paul took Christianity from Jerusalem to Rome. Instead, he shows that the true origins of Christianity lie further east, and that at one point it was poised to triumph in Asia, maybe even in China. The headquarters of Christianity might well have been Baghdad not Rome, and if that had happened then Western Christianity would have been very different.

The most famous – and perhaps most misunderstood – episodes in the epic history of the Holy Wars that are known to history as The Crusades – the clash between Richard the Lionheart and Saladin. In July 1192, Richard the Lionheart stood poised for a strike on Jerusalem, while Saladin – mighty sultan of Islam – readied his troops inside the city, preparing for the inevitable attack. During a year-long campaign across Palestine, these two legendary leaders had fought each other to a stand-still. Thousands had perished, appalling atrocities had been perpetrated on both sides. And now they faced each other in a battle for their sacred objective.

Dr. Thomas Asbridge introduces the epic story of the Crusades – a tale of religious fanaticism and unspeakable brutality, of medieval knights and Jihadi warriors; of castles and kings; of heroism, betrayal, and sacrifice. He explains how, using fresh evidence, eye-witness testimonies and contemporary accounts – from both the Christian and Islamic worlds – we are able to re-examine this epic medieval drama, and how he has retraced the steps of the Crusaders from a small town in France to the magnificent cities of the Holy Land, bringing to life the human experience of the Crusades, and shedding new light on how it was that two of the world’s great religions waged war in the name of God.

In the fourth episode of the series, Clovis was the first Frankish king to acknowledge the Christian faith. This changed the direction of Europe's history.

At a crucial time in history, when religious violence is impacting peace all over the world, and science is venturing into areas that were once the realms of faith, Morgan Freeman embarks on a journey around the globe and through the centuries to uncover the Story of God. He will explore different cultures and religions on the ultimate quest to uncover the meaning of life, God and all these big questions in between. In the first episode, the actor examines religious belief. He starts by discussing the afterlife with scientists, scholars, a Hindu monk and a man who had a near-death experience.