Eugène Emmanuel Viollet-le-Duc (French: [øʒɛn vjɔlɛlədyk]; 27 January 1814 – 17 September 1879) was a French architect and author who restored many prominent medieval landmarks in France, including those which had been damaged or abandoned during the French Revolution. His major restoration projects included Notre Dame Cathedral, the Basilica of Saint Denis, Mont Saint-Michel, Sainte-Chapelle, and the medieval walls of the city of Carcasonne. His later writings on the relationship between form and function in architecture had a notable influence on a new generation of architects, including Antonio Gaudi, Victor Horta, and Louis Sullivan.
Viollet-le-Duc was born in Paris in 1814, in the last year of the Empire of Napoleon Bonaparte His grandfather was an architect, and his father was a high-ranking civil servant, who in 1816 became the overseer the royal residences of Louis XVIII. His uncle Étienne-Jean Delécluze, was a painter, a former student of Jacques-Louis David, an art critic and hosted a literary salon, which was attended by by Stendhal and Sainte-Beuve. His mother hosted her own salon, which women could attend as well as men. There, in 1822 or 1823, Eugene met Prosper Merimée, a writer who would play a decisive role in his career.  
In 1825 he began his education at the Pension Moran, in Fontenay-aux-Roses. He returned to Paris in 1829 as a student at the College de Bourbon (now the Lycée Condorcet). He passed his baccalaureate examination in 1830. His uncle urged him to enter the École des Beaux-Arts, which had been created in 1806, but the École had an extremely rigid system, based entirely on copying classical models, and Eugene was not interested. Instead he decided to get practical experience in the architectural offices of Jacques-Marie Huvé and Achille Leclère, while devoting much of his time to drawing medieval churches and monuments around Paris.
He participated in the July 1830 revolution which overthrew Louis XVIII, building a barricade, his first known construction project. Following the revolution, which brought Louis Philippe to power, his father became chief of the bureau of royal residences. The new government created, for the first time, the position of Inspector General of Historic Monuments. Eugene's uncle Delescluze agreed to take Eugene on a long tour of France to see monuments. They traveled from July to October 1831 throughout the south of France, and he returned with a large collection of detailed paintings and watercolors of churches and monuments.
On his return to Paris, he moved with his family into the Tuileries Palace, where his father was now governor of royal residences. His family again urged him to attend the École des Beaux-Arts, but he still refused. He wrote in his journal in December 1831, "the Ecole is just a mold for architects. they all come out practically identical."  He was a talented and meticulous artist; He traveled around France to visit monuments, cathedrals, and other medieval architecture, made detailed drawings and water colors, which he sometimes sold at a high priceto members of the Court. 
On May 3, 1834, at age twenty, he married Élisabeth Templier, and in the same yer he was named an associate professor of ornamental decoration at the Royal School of Decorative Arts, which gave him a more regular income. With the money from the sale of his drawings and paintings, the couple set off on a long tour of the monuments of Italy, visiting Rome, Venice, Florence and other sites, drawing and painting. His reaction to the leaning tower of Pisa was characteristic: "It was extremely disagreeable to see", he wrote, "it would have been infinitely better if it had been straight."  In 1838, he presented several of his drawings at the Paris Salon, and began making a travel book, Picturesque and romantic images of the old France, for which, between 1838 and 1844, he made nearly three hundred engravings.
In October 1838, with the recommendation of Achille Leclère, the architect with whom he had trained, he was named deputy inspector of the enlargement of the Hotel Soubise, the new home of the French National Archives. His uncle, Delescluze, then recommended him to the new Commission of Historic Monuments of France, led by Prosper Merimée, who had just published a book on medieval French monuments. Though was just twenty-four years old and had no degree in architecture, he was asked to go to Narbonne to propose a plan for the completion of the cathedral there. He made his first plan, which included not only the completion but also the restoration of the oldest parts of the structure. His first project was rejected by the local authorities as too ambitious and too expensive.
His next project was a restoration of the Vézelay Abbey, the church of a Benedictine monastery founded in the 12th century to house the reputed relics of Mary Magdalene. The church had been sacked by the Huguenots in 1569, and during the French Revolution, the facade and statuary on the facade was destroyed. The vaults of the roof were weakened, and many of the stones had been carried off for other projects. When Merimée visited to inspect the structure; he heard stones falling around him. In February 1840 Merimée gave Viollet-le-duc the mission of restoring and reconstructing the church so it would not collapse, while "respecting exactly in his project of restoration all the ancient dispositions of the church." 
The task was all the more difficult because up until that time no scientific studies had been made of medieval building techniques, and there were no schools of restoration. He had no plans of the original building to work from. Viollet-le-Duc had to discover the flaws of construction that had caused the building to start to collapse in the first place, and to construct a more solid and stable structure. He lightened the roof and built new arches and to stabilize the structure, and slightly changed the shape of the vaults and arches. He was criticized for these modifications in the 1960s, though, as his defenders argued, without them the roof would have collapsed under their own weight. 
Mérimée's deputy, Lenormant, inspected the construction and reported to Mérimée: "The young Leduc seems entirely worthy of your confidence. He needed a magnificent audacity to take charge of such a desperate enterprise; it's certain that he arrived just in time, and if we had waited only ten years the church would have been a pile of stones." 
Viollet-le-Duc's success at Vezelay soon led to a series of much more ambitious projects. In 1840, in collaboration with his friend the architect Jean-Baptiste Lassus he began the restoration of Sainte-Chapelle in Paris; in 1844, he and Lassus were named the architects for the restoration of Notre Dame Cathedral. In 1847, he began the restoration of the Basilica of Saint-Sernin in Toulouse, and of the Basilica of Saint-Denis just outside Paris. In 1849, he began the restoration of the medieval ramparts of the city of Carcassonne and Amiens Cathedral. He also supervised the restoration of Mont Saint-Michel. During the Second Empire of Napoleon III, he understood the restoration of the Château de Pierrefonds and the Cathedral of Amiens, and Roquetaillade castle 
Besides his restorations, he also designed new buildings and structures, including The Church of Saint Denis de l'Estree in Saint-Denis, Seine-Saint-Denis, and the new facade of the Cathedral of Clermont-Ferrand. He presented a project for the new Opera House of Paris, but his project was rejected in favor of a more eclectic design by Charles Garnier. He also designed furniture, stained glass windows, and tombs, and additionally taught at the School o Drawing of the City of Paris.
Viollet-le-Duc famously defined restoration in his Dictionnaire of 1858: "To restore a building is not to maintain it, repair it or remake it: it is to re-establish it in a complete state which may never have existed at any given moment." He then explained that it had to meet three conditions: (1) The "re-establshment" had to be scientifically documented with plans and photographs and archeological records, which would guarantee exactness. (2) The restoration had to involve not just the appearance of the monument, or the effect that it produced, but also its structure; it had to use the most efficient means to assure the long life of the building, including using more solid materials, used more wisely. (3) the restoration had to exclude any modification contrary to obvious evidence; but the structure could be adapted to conform to more modern or rational uses and practices, which meant alterations to the original plan; and (4) The restoration should preserve older modifications made to the building, with the exception of those which compromised its stability or its conservation, or those which gravely violated the value its historical presence.
Viollet-le-Duc's restorations frequently combined historical fact with creative modification. For example, under his supervision, Notre Dame was not only cleaned and restored but also modified. The flèche, or spire, which had been constructed in about 1250, was torn down during the French Revolution. Viollet-le-Duc rebuilt a spire which was taller and of a slightly different style, to be more harmonious with the rest of the architecture. Another of his most famous restorations, the medieval fortified town of Carcassonne, was similarly enhanced, gaining atop each of its many wall towers a set of pointed roofs that are actually more typical of northern France. Many of these reconstructions were controversial. Viollet-le-Duc wanted what he called ‘a condition of completeness' which never actually existed at any given time. This approach to restoration was particularly problematic when buildings survived in a mixture of styles. For instance, Viollet-le-Duc eliminated eighteenth-century additions to Notre Dame. Both his theory and his practice were strongly criticized on the grounds that only what had once been in place should be reconstructed. At the same time, in the cultural atmosphere of the Second Empire theory necessarily became diluted in practice: Viollet-le-Duc provided a Gothic reliquary for the relic of the Crown of Thorns at Notre-Dame in 1862, and yet Napoleon III also commissioned designs for a luxuriously appointed railway carriage from Viollet-le-Duc, in the 14th-century Gothic style.
Notre Dame de Paris (restored 1845-1870)
The keep of the Chateau de Vincennes, (restored in the 1860s)
The walled town of Carcasonne (restored 1853-1879)
Chateau de Pierrefonds (restored 1857-1885)
Lausanne Cathedral, Switzerland (Restored 1874-1910)
Basic intervention theories of historic preservation are framed in the dualism of the retention of the status quo versus a "restoration" that creates something that never actually existed in the past. John Ruskin was a strong proponent of the former sense, while his contemporary, Viollet-le-Duc, advocated for the latter instance. Viollet-le-Duc wrote that restoration is a "means to reestablish [a building] to a finished state, which may in fact never have actually existed at any given time." The type of restoration employed by Viollet-le-Duc, in its English form as Victorian restoration, was decried by Ruskin as "a destruction out of which no remnants can be gathered: a destruction accompanied with false description of the thing destroyed."
This argument is still a current one when restoration is being considered for a building or landscape. In removing layers of history from a building, information and age value are also removed which can never be recreated. However, adding features to a building, as Viollet-le-Duc also did, can be more appealing to modern viewers.
Throughout his career Viollet-le-Duc made notes and drawings, not only for the buildings he was working on, but also on Romanesque, Gothic and Renaissance buildings that were to be soon demolished. His notes were helpful in his published works. His study of medieval and Renaissance periods was not limited to architecture, but extended to furniture, clothing, musical instruments, armament, geology and so forth.
All this work was published, first in serial, and then as full-scale books, as:
Viollet-le-Duc is considered by many to be the first theorist of modern architecture. Sir John Summerson wrote that "there have been two supremely eminent theorists in the history of European architecture - Leon Battista Alberti and Eugène Viollet-le-Duc."
His architectural theory was largely based on finding the ideal forms for specific materials, and using these forms to create buildings. His writings centered on the idea that materials should be used 'honestly'. He believed that the outward appearance of a building should reflect the rational construction of the building. In Entretiens sur l'architecture, Viollet-le-Duc praised the Greek temple for its rational representation of its construction. For him, "Greek architecture served as a model for the correspondence of structure and appearance." There is speculation that this philosophy was heavily influenced by the writings of John Ruskin, who championed honesty of materials as one of the seven main emphases of architecture.
Another component in Viollet-le Duc's theory was how the design of a building should start from its program and the plan, and end with its decorations. If this resulted in an asymmetrical exterior, so be it. He dismissed the symmetry of classicist buildings as vain, caring too much about appearances at the expense of practicality and convenience for the inhabitants of the house.
In several unbuilt projects for new buildings, Viollet-le-Duc applied the lessons he had derived from Gothic architecture, applying its rational structural systems to modern building materials such as cast iron. He also examined organic structures, such as leaves and animal skeletons, for inspiration. He was especially interested in the wings of bats, an influence represented by his Assembly Hall project.
Viollet-le-Duc's drawings of iron trusswork were innovative for the time. Many of his designs emphasizing iron would later influence the Art Nouveau movement, most noticeably in the work of Hector Guimard, Victor Horta, Antoni Gaudí or Hendrik Petrus Berlage. His writings inspired some American architects, including Frank Furness, John Wellborn Root, Louis Sullivan, and Frank Lloyd Wright.
Viollet-le-Duc had a second career in the military, primarily in the defence of Paris during the Franco-Prussian War (1870–71). He was so influenced by the conflict that during his later years he described the idealized defense of France by the analogy of the military history of Le Roche-Pont, an imaginary castle, in his work Histoire d'une Forteresse (Annals of a Fortress, twice translated into English). Accessible and well researched, it is partly fictional.
Annals of a Fortress strongly influenced French military defensive thinking. Viollet-le-Duc's critique of the effect of artillery (applying his practical knowledge from the 1870–1871 war) is so complete that it accurately describes the principles applied to the defence of France until World War II. The physical results of his theories are present in the fortification of Verdun prior to World War I and the Maginot Line prior to World War II. His theories are also represented by the French military theory of "Deliberate Advance", such that artillery and a strong system of fortresses in the rear of an army are essential.
Some of his restorations, such as that of the Château de Pierrefonds, have become very controversial because they were not intended so much to recreate a historical situation accurately as to create a "perfect building" of medieval style: "to restore an edifice", he observed in the Dictionnaire raisonné, "is not to maintain it, repair or rebuild it, but to re-establish it in a complete state that may never have existed at a particular moment". The idea and the very word restoration applied to architecture Viollet-le-Duc considered part of a modern innovation. Modern conservation practice considers Viollet-le-Duc's restorations too free, too personal, too interpretive, but some of the monuments he restored might have been lost otherwise.
The English architect Benjamin Bucknall (1833–95) was a devotee of Viollet-le-Duc and during 1874 to 1881 translated several of his publications into English to popularise his principles in Great Britain. The later works of the English designer and architect William Burges were greatly influenced by Viollet-le-Duc, most strongly in Burges's designs for his own home, The Tower House in London's Holland Park district and Burges's designs for Castell Coch near Cardiff, Wales.
An exhibition, Eugène Viollet-le-Duc 1814–1879 was presented in Paris, 1965, and a larger, centennial exhibition, 1980.
In 1874 Viollet-le-Duc resigned as diocesan architect of Paris, and was succeeded by his contemporary, Paul Abadie. In his old age, Viollet-le-Duc relocated to Lausanne, Switzerland, where he constructed a villa (since destroyed). He died there in 1879.