In the second episode of his series tracing the story of the most famous trade route in history, Dr Sam Willis travels west to central Asia, a part of the Silk Road often overlooked and yet the place of major innovations, big historical characters and a people - the Sogdians - whose role was pivotal to its success. In the high mountain passes of Tajikistan, Sam meets the last survivors of that race, who once traded from the Mediterranean to the China Sea. In the Uzbek cities of Samarkand and Bukara, he discovers how they were built by armies of captive craftsmen for one of the greatest conquerors the world has ever seen - Timur. From here, Sam follows the flow of goods back towards the markets of the west, showing how their trading culture sparked cultural, technical and artistic revolutions all along the Silk Road, and goes back to school to learn where modern mathematics and astronomy were born.