ribs of the vaulted ceiling; a mid-level gallery, or triforium, with windows; and an upper level, or clerestory, with tall windows filling the upper walls with glass. The nave has a height of 29 meters, but a width less than many cathedrals, probably due to the re-use of an earlier Romanesque foundation. The vaults are covered with the original roof structure, built of wooden beams from the 13th century in the choir, and from the 15th century in the nave. The choir still has its original fifteen 13th-century windows, which feature both scenes of the lives of Christ, Apostles and Saints, as well as windows which depict the professions of the guilds which contributed to the financing of the windows. The rose window in the north transept, built in the early 14th century, has an unusual design. It was placed into the center of a square already filled with stained glass. This later caused difficulties of stability; a buttress had to be built in the interior, across the middle of the window, which divides it into two. The window is also supported by flying buttresses on the outside. The south transept also has a rose window, and contains the original case of the 16th century organ, It was donated by Martin de Beaune, and built by Barnabé Delanoue. It now contains an 18th-century organ built by Cliquot. Art and Decoration The nave contains a monumental tomb, that of the two children of King Charles VIII of France and Anne of Brittany, who died as infants. It was made in 1506 by Guillaume Regnault or Girolamo da Fiesole, and originally was located in the church of St. Martin, and was moved to the cathedral after the French Revolution. The tomb is made of Carrara marble, in the Italian style. The recumbent statues are reminiscent of the 15th-century French medieval tradition (school of Michel Colombe). Stained glass In the 13th century, the artists working on Tours Cathedral launched a small revolution in the design of stained glass windows. Instead of having the entire window filled a multitude of small scenes made of tiny pieces of deeply-coloured glass, the Tours artists began making windows with a mixture of types of glass; the traditional iconographic scenes with Biblical figures were surrounded by panes of clear or lightly coloured glass decorated with ornamental and vegetal themes. This served the purpose of bringing a much greater