But these qualities always result from the greatest regularity of the forms and rationality of their relations. Therefore beautiful architecture selects only regular figures composed of straight lines or regular curves, and also the bodies which result from these, such as cubes, parallelopipeda, cylinders, spheres, pyramids, and cones; but as openings sometimes circles or ellipses, yet, as a rule, quadrates, and still oftener rectangles, the latter of thoroughly rational and very easily comprehended relation of their sides (not, for instance as 6:7, but as 1:2, 2:3), finally also blind windows or niches of regular and comprehensible proportions. For the same reason it will readily give to the buildings themselves and their large parts a rational and easily comprehended relation of height and breadth; for example, it will let the height of a facade be half the breadth, and place the pillars so that every three or four of them, with the intervals between them, will measure a line which is equal to the height, thus will form a quadrate. The same principle of perceptibility and easy comprehension demands also that a building should be easily surveyed. This introduces symmetry, which is further necessary to mark out the work as a whole, and to distinguish its essential from its accidental limitation; for sometimes, for example, it is only under the guidance of symmetry that one knows whether one has before one three buildings standing beside each other or only one. Thus only by means of symmetry does a work of architecture at once announce itself as individual unity, and as the development of a central thought.