Istanbul is famously, the only city in the world to straddle two continents - Europe and Asia. The dividing line is the Bosphorus.
Edward Stourton has been exploring the life and rich history of this stretch of water, which is 31 kilometers long. The Bosphorus gives Istanbul its unique character.
But, as we hear in this last programme of the series, having a foot in both Europe and Asia, forces the people who live there to ask themselves interesting questions about their religious identity and the future of Turkey.
(Image: View from he Bosphorus of the Istanbul skyline)