simple lancet windows, including the Five Sisters in the north transept. These are five lancets, each tall and five feet wide and glazed with grey (grisaille) glass, rather than narrative scenes or symbolic motifs that are usually seen in medieval stained-glass windows. In the south transept is a rose window whose glass dates from about 1500 and commemorates the union of the royal houses of York and Lancaster. The roofs of the transepts are of wood; that of the south transept was burnt in the fire of 1984 and was replaced in the restoration work which was completed in 1988. New designs were used for the bosses, five of which were designed by winners of a competition organised by the BBC's Blue Peter television programme. Work began on the chapter house and its vestibule that links it to the north transept after the transepts were completed. The style of the chapter house is of the early Decorated Period where geometric patterns were used in the tracery of the windows, which were wider than those of early styles. However, the work was completed before the appearance of the ogee curve, an S-shaped double curve that was extensively used at the end of this period. The windows cover almost all of the upper wall space, filling the chapter house with light. The chapter house is octagonal, as is the case in many cathedrals, but is notable in that it has no central column supporting the roof. The wooden roof, which was of an innovative design, is light enough to be able to be supported by the buttressed walls. The chapter house has many sculptured heads above the canopies, representing some of the finest Gothic sculpture in the country. There are human heads, no two alike, and some pulling faces; angels; animals and grotesques. Unique to the transepts and chapter house is the use of Purbeck marble to adorn the piers, adding to the richness of decoration. The chapter house exhibits the influence of Saint-Urbain, Troyes in the tracery in the vestibule, while the stalls are enlarged versions of the archivolt niches in the portal of Notre-Dame de Paris. The nave was built between 1291 and and is also in the decorated Gothic style. It is the widest Gothic nave in England and has a wooden roof (painted so as to appear like stone) and the aisles have vaulted stone roofs. At its