Gothic architecture had its most brilliant expression in the early part of this period, degenerating later largely through an exaggeration of its elements. At the end of the thirteenth century Castilian Gothic may be said to have differed from that of the other European countries in the following respects: its maintenance of classical proportions, with scant difference between the length and width of an edifice, reducing the height; less development in the use of windows; greater robustness of walls, columns, and piers, diminishing the importance of buttresses; more nearly flat roofs; and the general use and ample size of cloisters in convents and churches. The structural basis and sober character of early Gothic began to be lost sight of in the fourteenth century, and, in particular, ornamentation was used without any relation to structural needs. The corruption of Gothic became more and more marked in the fifteenth century, when proportions and structural ideals were forgotten, and adornment, notably in the use of pinnacles, was employed in excessive degree. It was at this time that the choir of Spanish cathedrals was moved to the centre of the nave, in front of the high altar. This was the greatest age of Gothic civil and military art, especially of the latter. Castles were more solidly and more richly built, with handsome towers and other exterior defences and with embattled walls. Towers and battlements also appeared on the walls of cities. Mudéjar architecture continued to develop, notably in Toledo and Seville, in both religious and civil edifices, and some of the best specimens of this art date from the fourteenth and fifteenth centuries. It was especially employed in the interior decoration of palaces and private houses,--in panelling, handsomely worked wooden roofs, painted and sculptured friezes, and the use of tiles. On the outside it appeared in eaves and beams of brightly colored woods. [Sidenote: The lesser arts.]