IT is in the distinction between the wall surfaces which were preserved by Italian buildings and those of the North, which were distributed into window openings and buttresses, that we find a connection with the topic of Italian painting and the architectural conditions of its development.
The Byzantine and early Christian system of church building was one of small window openings, placed as far as possible in the upper portions of the building, and of large interior surfaces devoted to the gorgeous color effects of the mosaics. The Italians of the fourteenth century abandoned the mosaics, but they replaced them by wall frescoes (paintings on plaster), and their system of wall surfaces required for the frescoes was the same as that required for mosaics. It is here that the real break with the style of the North is apparent. The northern buttress was essentially necessary as the support of a vaulted ceiling which otherwise lacked the necessary supporting walls; for the development of the window openings amounted to the absence of the wall. In other words, the demand for frescoes explains the Italian Gothic in so far, at least, as the preservation of the wall surface and the absence of large window openings are concerned.
The system of stained glass decoration shows the to-____________________