§ VI. The proper forms of this superimposition of weight on lightness have arisen, for the most part, from the necessity or desirableness, in many situations, of elevating the inhabited portions of buildings considerably above the ground level, especially those exposed to damp or inundation, and the consequent abandonment of the ground story as unserviceable, or else the surrender of it to public purposes. Thus, in many market and town houses, the ground story is left open as a general place of sheltered resort, and the enclosed apartments raised on pillars. In almost all warm countries the luxury, almost the necessity, of arcades to protect the passengers from the sun, and the desirableness of large space in the rooms above, lead to the same construction. Throughout the Venetian islet group, the houses seem to have been thus, in the first instance, universally built, all the older palaces appearing to have had the rez de chaussée perfectly open, the upper parts of the palace being sustained on magnificent arches, and the smaller houses sustained in the same manner on wooden piers, still retained in many of the cortiles, and exhibited characteristically throughout the main street of Murano. As ground became more valuable and house-room more scarce, these ground-floors were enclosed with wall veils between the original shafts, and so remain; but the type of the structure of the entire city is given in the Ducal Palace. § VII. To this kind of superimposition we owe the most picturesque street effects throughout the world, and the most graceful, as well as the most grotesque, buildings, from the many-shafted fantasy of the Alhambra (a building as beautiful in disposition as it is base in ornamentation) to the four-legged stolidity of the Swiss Chalet:[60] nor these only, but great part of the effect of our cathedrals, in which, necessarily, the close triforium and clerestory walls are superimposed on the nave piers; perhaps with most majesty where with greatest simplicity, as in the old basilican types, and the noble cathedral of Pisa. § VIII. In order to the delightfulness and security of all such arrangements, this law must be observed:--that in proportion to the height of wall above them, the shafts are to be short. You may take your given height of wall, and turn any quantity of that wall into shaft that you like; but you must not turn it all into tall shafts, and then put more wall above. Thus, having a house five stories high, you may turn the lower story into shafts, and leave the four stories in wall; or the two lower stories into shafts, and leave three in wall; but, whatever you add to the shaft, you must take from the wall. Then also, of course, the shorter the shaft the thicker will be its _proportionate_, if not its actual, diameter. In the Ducal Palace of Venice the shortest shafts are always the thickest.[61]