Napoleon III also began or completed the restoration of several important historic landmarks, carried out for him by Eugène Viollet-le-Duc. He restored the flèche, or spire, of the Cathedral of Notre-Dame de Paris, which had been partially destroyed and desecrated during the French Revolution. In 1855, he completed the restoration, begun in 1845, of the stained glass windows of the Sainte-Chapelle, and in 1862, he declared it a national historical monument. In 1853, he approved and provided funding for Viollet-le-Duc's restoration of the medieval town of Carcassonne. He also sponsored Viollet-le-Duc's restoration of the Château de Vincennes and the Château de Pierrefonds, In 1862, he closed the prison which had occupied the Abbey of Mont-Saint-Michel since the French Revolution, where many important political prisoners had been held, so it could be restored and opened to the public.