The world's largest palace, the Forbidden City, stands at the heart of Chinese history, as the home to the emperors for 600 years. And it's full of secrets. This documentary goes behind closed doors to explore this extraordinary palace-city and to discover the clues to its creation. Unique access to the latest conservation works uncovers evidence hidden in locked halls and high in the mighty roofs, revealing a ruler who governed by fear but also created an exquisite and enormous work of art and technology. Tests on the paints reveal trade with Europe, and the programme experiments with an ice road to move an entire marble stairway. And another huge experiment tests the Forbidden City to destruction, as a giant scale model is placed on a seismic shake table to replicate the earthquakes that shook Beijing and to explore the design secrets that enabled the Forbidden City to stand up to the greatest shocks on earth.