Nevertheless, the development was very great, and is to be explained, very largely, by social causes, such as the advance in the population and importance of the cities and of the middle class. Greater cathedrals were therefore needed, but they were also desired from motives of vanity, which prompt new social forces to construct great monuments. The cathedrals became not only a religious centre but also a place of meeting for the discussion of business and political affairs, the heart and soul of the cities in which they were located. Gothic architecture also manifested itself in military and civil edifices. The castle was the characteristic type of the former. The material now became stone, instead of wood. As in other parts of Europe, there were the surrounding moat and the bridge, the walls with their salients and towers, the buildings inside for the artisans on the one hand, and for the lord and his soldiers on the other, and the powerfully built tower of homage to serve as a last resort. The growth of the towns gave rise to the erection of local government buildings, or town halls, and private dwellings began to have an important architectural character. Another style of architecture, usually called Mudéjar, existed in this period, combining Arabic with Christian elements, of which the latter were Gothic of a simplified character. The roof was of wood, but with the ornamentation of the period. The body of the edifice was of brick, which was left without covering on the outside, giving a reddish tone to the building. Sculpture had an important vogue as an adjunct of architecture. Gradually, it passed from the badly proportioned, stiff figures of the earlier years to something approaching realism and to a great variety of form. Painting was notable only for its use in the adornment of manuscripts and of windows, and in these respects the work done was of a high order. Both sculpture and painting were employed to represent sacred history or allegory. Rich tiles were much used, both in the form of azulejos, and in that of compositions of human figures, in which the usual symbolism appeared. The gold work and furniture also bore witness to the greater wealth of this period as compared with earlier times. _Aragon, Catalonia, and Valencia_ [Sidenote: Economic differences in the kingdom of Aragon.] [Sidenote: Catalan commerce.]