The 13th century was known as the golden age of castle building, when dynastic struggles and the threat of warfare created increasingly larger, mightier defensive structures.

Most are still standing to this day. But many of the secrets of how they were constructed have been lost in time. How were they built? What methods were used? And why do they still stand today?

Historian Ruth Goodman and archaeologists Tom Pinfold and Peter Ginn travel to the Burgundy region of France, to Guedelon Castle, where a medieval castle is being built using only the tools, techniques and materials of the 13th century. Guedelon is the world's biggest archaeological experiment - a 25-year quest to learn the forgotten skills and expertise of medieval castle builders.

The team experience daily life as castle workers, learning how ancient crafts and early engineering were put to use in constructing these mighty fortresses, how warfare determined castle design, what went on inside the walls and how the medieval world was far more informed, colourful and ingenious than we often believe. Show less