The Château de Châteaubriant is a medieval castle strongly modified during the Renaissance, located in the commune of Châteaubriant in the Loire-Atlantique département of France. The original castle was founded in the 11th century on the eastern border of Brittany and, such as the fortresses in Vitré, Fougères, Ancenis and Clisson, it was defending the duchy against Anjou and the Kingdom of France.