Watch HDToday. In the heart of Paris, Île de la Cité once featured one of the most majestic palaces of medieval times: The Palais des Rois. Built in the early Middle Ages, only two parts of this grandiose palace remain: The Sainte-Chapelle, the largest and most daring palatial chapel of the time; and the Conciergerie, a medieval room of impressive dimensions, known for having served as a prison and housing the jails of Marie-Antoinette.