As will be observed, the whole of the buttresses are internal, as is very generally the case in the South; and where painted glass is not used, and fresco painting is the principal mode of decoration, such a system has many advantages. The outer walls are scarcely ever seen, and by this arrangement great internal extent and appearance of gigantic strength is imparted, while the whole space covered by the building is available for internal use. But where painted glass is the principal mode of decoration, as was the case to the north of the Loire, such a system was evidently inadmissible. Then the walls were internally kept as flat as possible, so as to allow the windows to be seen in every direction, and all the mechanical expedients were placed on the outside. Admirably as the Northern architects managed all this, I cannot help thinking, if we leave the painted glass out of the question, that the Southern architects had hit on the more artistic arrangement of the two; and where, as at Alby, the lower parts of the recesses between the internal buttresses were occupied by deep windowless chapels, and the upper lights were almost wholly concealed, the result was an extraordinary appearance of repose and mysterious gloom. This character, added to its simplicity and the vastness of its vaults, render Alby one of the most impressive churches in France, and a most instructive study to the philosophical inquirer into the principles of effect, as being a Gothic church built on principles not only dissimilar from, but almost diametrically opposed to, those which we have been usually accustomed to consider as indispensable, and as inherent requisites of the style. [Illustration: 569. Plan of Church of the Cordeliers, at Toulouse. Scale 100 ft. to 1 in.]