It wasn't until the 19th century before the Cathedral was fully restored thanks in part to the writer Victor Hugo, who with his book 'Notre-Dame de Paris', made the Parisians realise the cathedral was worth restoring. The 20 year long restoration was led by a local architect, Eugène Emmanuel Viollet-le-Duc. Viollet-le-Duc made drastic, controversial modifications to the building and even added a spire. The cathedral was restored again between 1991 and 2001, this time the historic architecture was carefully preserved.