Eugène-Emmanuel Viollet-le-Duc was a 19th century French architect known for his restoration of medieval buildings and development of architectural theory. Some of his most notable restorations included Notre Dame Cathedral in Paris, Carcassonne fortress, and Sainte-Chapelle. His philosophy of restoration emphasized completeness over historical accuracy, believing buildings should be returned to a hypothetically complete state. Viollet-le-Duc's writings and restorations had a significant influence on later architects and helped establish principles of architectural preservation.