Prof Michael Livingstone investigates Richard the Lionheart's medieval super fortress.

At the end of the 12th century, tensions between England and France were growing. The two kings, the ambitious Philippe II of France and the warrior Richard the Lionheart of England, had once been great allies but now were sworn enemies, each determined to destroy the other.

On the frontline of the conflict was a brand new English castle built on French soil, mighty Chateau Gaillard. Today, it stands in ruins, but it remains an impressive bastion dominating the landscape. This wasn’t just an English castle. It was a statement of military intent and an engineering marvel - a memorial in stone to the Lionheart.

How was it built? History Hit goes to the extraordinary castle building project at Guedelon to find out how to make a fortress.

Michael digs into the dramatic history of Chateau Gaillard, exploring what happened during the bloody siege that took place here. Why was Chateau Gaillard so important that Richard himself referred to it as his fair castle upon the rock?