two levels of the lantern tower and added flamboyant decoration and sculpture. Another fire in 1822 destroyed the lead and wood spire, which was then replaced, after much controversy, by the architect Jean-Antoine Alavoine with a tower of iron and copper, finished in 1882. He surrounded the new spire with four smaller spires, made of copper. One of these fell during a hurricane in 1999, going through the roof and damaging the choir stalls below. Tourelles and sculpture galleries In the 13th century four smaller towers, or tourelles, with spires, were added atop the buttresses that were built to support the west front, two on either side of the central portal below. In the 14th century, to enrich the decoration even further, three gables were attached to the west front below each of the tourelles. The gables were filled with sculpture; over the north portal, statues of the first archbishops, apostles and saints, and on the south, kings and prophets from the Old Testament. They added another layer to the almost incredible complexity of the west front. The Nave exterior Flying buttresses along the north and south sides of the cathedral reach up over the roof of the collateral aisles to support the upper walls of the nave. The space between the buttresses on the lower level is filled with collateral chapels. Thanks to the support of the buttresses, the upper walls of the nave are entirely filled with windows. The edges of the roof of the collateral aisles and of the nave are both lavishly decorated with balustrades and pinnacles. balancing the horizontal and vertical elements. North transept Two portals, on the north and the south, very lavishly decorated, give access to the transept, at the meeting point between the nave and the choir. On the north is the portail des librairies, and to the south the portail de la Calende. The north portal is similar in its plan to the north transept portal of Notre-Dame-de-Paris, built a few years earlier; the decoration of the portals spills over into the adjacent sections. Each portal has a column-statue between the doors, and is topped by a tympanum full of sculpture, and above that an arched voussure filled with three bands of statues. Above this a lace-like pointed gable, which rises upward in front of the windows of the claire-voie gallery as far as the rose window. A similar sculpted gable