Who spread Christianity, how, and why? In her quest to find the answer, Professor Alice Roberts takes us on a gripping investigative journey. From a secluded valley in south Wales to the shores of Brittany; from the heart of the Roman Empire in a time of political turmoil to the ancient city of Corinth in the footsteps of the apostle Paul; from Alexandria in the fourth century to Constantinople.

As the Roman Empire crumbled in Western Europe, a shadow of power remained, almost perfectly mapping onto its disappearing territories. And then, it continued to spread. Unearthing the archaeological clues and challenging long-established histories, Professor Roberts tells a remarkable story about the relationship between the Roman Empire and Christianity.