Eugène-Emmanuel Viollet-le-Duc was a 19th century French architect known for his restoration of Gothic buildings and development of architectural theory. Some of his most prominent restorations included Notre Dame Cathedral in Paris, the walled city of Carcassonne, and Sainte-Chapelle. Viollet-le-Duc's philosophy of restoration emphasized completing buildings to a state that may have never existed, using his imagination. While controversial, his restorations and writings significantly influenced later architects and spread appreciation for Gothic architecture.