By far the most important specimens of Gothic architecture are the cathedrals and large churches which were built during the prevalence of the style. They were more numerous, larger, and more complete as works of art than any other structures, and accordingly they are to be considered on every account as the best examples of pointed architecture. [Illustration: FIG. 2.--GROUND PLAN OF PETERBOROUGH CATHEDRAL. (1118 to 1193.) A. Nave. B B. Transepts. C. Choir. D D. Aisles. E. Principal Entrance.] [Illustration: FIG. 3.--TRANSVERSE SECTION OF THE NAVE OF SALISBURY CATHEDRAL. (A.D. 1217).] The arrangement and construction of a Gothic cathedral were customarily as follows:--(See Fig. 2.) The main axis of the building was always east and west, the principal entrance being at the west end, usually under a grand porch or portal, and the high altar stood at the east end. The plan (or main floor) of the building almost always displays the form of a cross. The stem of the cross is the part from the west entrance to the crossing, and is called the nave. The arms of the cross are called transepts, and point respectively north and south. Their crossing with the nave is often called the intersection. The remaining arm, which prolongs the stem eastwards, is ordinarily called the choir, but sometimes the presbytery, and sometimes the chancel. All these names really refer to the position of the internal fittings of the church, and it is often more accurate simply to employ the term eastern arm for this portion of a church. The nave is flanked by two avenues running parallel to it, narrower and lower than itself, called aisles. They are separated from it by rows of columns or piers, connected together by arches. Thus the nave has an arcade on each side of it, and each aisle has an arcade on one side, and a main external wall on the other. The aisle walls are usually pierced by windows. The arches of the arcade carry walls which rise above the roofs of the aisles, and light the nave. These walls are usually subdivided internally into two heights or stories; the lower story consists of a series of small arches, to which the name of triforium is given. This arcade usually opens into the dark space above the ceiling or vault of the aisle, and hence it is sometimes called the blind story. The upper story is the range of windows already alluded to as lighting the nave, and is called the clerestory. Thus a spectator standing in the nave, and looking towards the side (Figs. 4 and 5), will see opposite him the main arcade, and over that the triforium, and over that the clerestory, crowned by the nave vault or roof; and looking through the arches of the nave arcade, he will see the side windows of the aisle. Above the clerestory of the nave, and the side windows of the aisles, come the vaults or roofs. In some instances double aisles (two on each side) have been employed.