In the final episode of his series tracing the story of the most famous trade route in history, Dr Sam Willis continues his journey west in Iran. The first BBC documentary team to be granted entry for nearly a decade, Sam begins in the legendary city of Persepolis - heart of the first Persian Empire. Following an ancient caravan route through Persia's deserts, he visits a Zoroastrian temple where a holy fire has burned for 1,500 years, and Esfahan, one of the Silk Road's architectural jewels and rival to Sam's next destination - Istanbul. In the ancient capital of ...