This Transition begins the decline of Gothic architecture from the perfect and symmetrical Decorated to the style which showed more elaborate and richer work, but was wanting in the elegant effect for which the Decorated Period stands unequalled. The Perpendicular Period is very much the longest in point of time, extending, as it did, over 170 years. The name is both descriptive and appropriate to the style, and the chief instrument by which this effect is produced is the straight-sided, shallow, sunk panelling. In previous times the panel had been used but sparingly, but now the whole surface, inside and outside, was covered with it. The beautiful flowing tracery of the Decorated Period was supplanted by the mullions, running, as a rule, straight up from the sill to the window top. The spaces between were frequently divided and subdivided by similar perpendicular lines, so that _perpendicularity_ is most distinctly the characteristic of these windows. In fact, by this subdivision the windows became simply an arrangement of panels, pierced to let in the light. As the tendency of the Perpendicular style is to employ the vertical line at the expense of the horizontal, a general squareness spread from the characteristic tracing and panelling to the other features and details. In the later examples of this period the arches of the windows and doorways became flattened, and the four-centred Tudor arch, so called because it was formed of curves described from four centres (Pl. 45, Fig. 4), began to be extensively used, until all beauty and proportion were lost, and stiffness and squareness became the striking characteristics of this style. The later windows had frequently great width in proportion to their height, and they were placed so near together that the wall space was reduced and the strength of the building entirely depended upon the buttresses. The windows were originally filled with painted glass, and the panel form of the subdivision lent itself admirably to this decoration. _Square-headed Windows_ (Pl. 45, Fig. 6) are frequent in this style, and the doorways were generally set in a square frame (Fig. 4), though many of the later doorways are frequently very rich in the decoration over them. The foliage employed in this style, by reason of its squareness, is much less beautiful than that of the Decorated Period. It has neither the vigour and beauty of the Early English nor the imitative skill of the Decorated. It is angular, shallow, and often wooden in appearance. An ornament used very extensively during this period was the so-called “Tudor ornament.” (Pl. 45, Fig. 7, and Pl. 46, Fig. 7.) It is founded on the fleur-de-lis alternate with a trefoil or ball, but although poor in invention, has frequently a very rich effect, as in Henry VII.’s chapel at Westminster.