332 COMPARATIVE ARCHITECTURE. In the Provinces, the principal examples are : — The greater portion of the Cathedrals of Norwich, Durham, Oxford, Gloucester, Exeter, Ely, Hereford, Peterborough, Winchester, S. Albans, Chichester, Waltham, and Tewkesbury Abbey. Barfreston Church, Kent, and Iffley Church, Oxon (No. 138), are good examples of small Norman churches. A. Plans. — The nave was considerably lengthened from the Saxon period, and transepts were employed, with usually a tower at the crossing. Most of the cathedrals date from this period, and the general type of plan laid down was developed rather than changed, great length being aimed at, as at Norwich, Durham, Ely, S. Albans, and Winchester. The chapel of the Tower of London (No. 135) is a type of a small chapel in the style. The towers are square and massive, as at S. Alban's Abbey and Iffley Church (No. 138). In Norfolk and Suffolk are some fifty churches, having at their west end round towers supposed to be due to Scandinavian influence, but probably owing to these being more readily con- structed, in the absence of suitable stone to form square angles. Castles, owing to the recent conquest, were numerous and important, commanding fords on the rivers, high roads, and other strategic points. The Tower of London gives a good idea of the system of defence adopted (No. 131 a). B. Walls. — ^These are very thick, and frequently arcaded in later work, but are often constructed with defective masonry, the core being imperfectly bonded with the facing. The interiors have nearly an equal height assigned to nave arcade, triforium, and clerestory, and a passage was often formed between the clerestory window and the triple arch carrying the inside of the wall, a method also adopted in the churches at Caen. Buttresses are broad and flat, with little projection (No. 141 a), and often flush with the corbel table, which supports a plain parapet (No. 136 a, b). c. Openings. — These were frequently formed with square recesses, known as "orders," to their jambs. The windows are usually small, narrow and deeply splayed, with semicircular heads. They are in single lights, but double windows divided by a shaft frequently occur in towers. Three openings, of which the centre one is largest, are sometimes grouped together. Doorways are deeply recessed and richly ornamented with the zigzag ornament and beak-head, as at Iffley Church, Oxon (No. 138), or elaborately carved with sculptural subjects, as at Barfreston, Kent. D. Roofs. — The vaulting was waggon-headed, or intersecting with plain groins (No. 112 g). The roof-trusses were of open tiujber, chiefly of king-post form,
