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.

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.

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.

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 Robert Bartlett explores the impact of the Normans on southern Europe and the Middle East. The Normans spread south in the 11th century, winning control of southern Italy and the island of Sicily. There they created their most prosperous kingdom, where Christianity and Islam co-existed in relative harmony and mutual tolerance. It became a great centre of medieval culture and learning. But events in the Middle East provoked the more aggressive side of the Norman character. In 1095, the Normans enthusiastically answered the Pope's call for holy war against Islam and joined the first crusade. They lay siege to Jerusalem and eventually helped win back the holy city from the muslims. This bloody conquest left a deep rift between Christianity and Islam which is still being felt to this day.

Ancient Greece's most powerful god wages an epic struggle against his father for control of the universe. It's the ultimate Clash of the Gods as the Olympians challenge the Titans in mythology's greatest showdown. This is a pivotal battle that experts believe may have been ancient code for a real world event - one of the greatest natural disasters the Earth ever experienced.