Boris Johnson travels around the Mediterranean to investigate the early beginnings of the long-running, if intermittent, antagonism between Christianity and Islam. It has often been said that the two religious cultures are locked in a never-ending cycle of mutual antipathy, distrust and violence. He not only looks at the clashes between the two civilisations, but also at the many periods of tolerance, interchange and co-operation. Over more than seven centuries before 1492 - when Spain was 'reconquered' by the Catholic monarchs - there were many conflicts between the two faiths. But the true historical picture reveals a far more complex relationship. In the two-part series, which was filmed before Boris became Mayor of London, he travels to Spain, France, Turkey, Syria, Israel and Egypt, examining the early history of Islam and the extraordinary chain of conquests in which it swept across the territories of Rome.