Tracing the story of the most famous trade route in history, Dr. Sam Willis reveals how an emperor's desire for silk spawned a network of trading paths that would span thousands of miles.

Over 50,000 years ago, people made the first open sea voyage in human history to discover Australia - a continent full of strange plants that had been evolving in isolation for 65 million years.

Nourished by rich nutrients carried hundreds of kilometres downstream, the Mekong's delta region is a biological treasure trove that is bustling with life.