Part of the art in arranging such a composition is to combine and yet contrast its horizontal and vertical elements. The horizontal lines, or features, are those which serve to bind the whole together, and the vertical ones are those which give that upward tendency which is the great charm and peculiar characteristic of Gothic architecture. It is essential for the masses of solid masonry and the openings to be properly contrasted and proportioned to each other, and here, as in every part of a building, such ornaments and ornamental features as are introduced must be designed to contribute to the enrichment of the building as a whole, so that no part shall be conspicuous either by inharmonious treatment, undue plainness, or excessive enrichment. [Illustration: FIG. 14.--HOUSE AT CHESTER. (16TH CENTURY.)] During the transition the gable became steeper in pitch than the comparatively moderate slope of Norman times. In the E. E. it was acutely pointed, in the Dec. the usual slope was that of the two sides of an equilateral triangle: in the Perp. it became extremely flat and ceased to be so marked a feature as it had formerly been. In domestic buildings the gable was employed in the most effective manner, and town dwelling-houses were almost invariably built their gable ends to the street (Fig. 14). * * * * * A very effective form of wall was frequently made use of in dwelling-houses. This consisted of a sturdy framework of stout timbers exposed to view, with the spaces between them filled in with plaster. Of this work, which is known as half-timbered work, many beautiful specimens remain dating from the fifteenth and following centuries (Figs. 14 and 15), and a few of earlier date. In those parts of England where tiles are manufactured such framework was often covered by tiles instead of being filled in with plastering. In half-timbered houses, the fire-places and chimneys, and sometimes also the basement storeys, are usually of brickwork or masonry; so are the side walls in the case of houses in streets. It was usual in such buildings to cause the upper storeys to overhang the lower ones. _Columns and Piers._ The columns and piers of a building virtually form portions of its walls, so far as aiding to support the weight of the roof is concerned, and are appropriately considered in connection with them. In Gothic architecture very little use is made of columns on the outside of a building, and the porticoes and external rows of columns proper to the classic styles are quite unknown. On the other hand the series of piers, or columns, from which spring the arches which separate the central avenues of nave, transepts and choir from the aisles, are among the most prominent features in every church. These piers varied in each century.[14]