This Flamboyant Gothic masterpiece was built by King Louis from 1230-38. It predates the Sainte Chapelle in Paris by 10 years and was probably designed by the same architect, Pierre de Montreuil, without its counterpart's stained-glass windows. Etched on the keystones are illustrations believed to depict the king, his mother Blanche de Castille and Marguerite de Provence. If this is the case, they would be the oldest surviving portraits of members of the royal family.