The proportional combinations of these elements are such that they cannot be methodically classified, and in this the architecture of Egypt is distinguished from that which we call classic. In Greek art there is a _modulus_ which determines the quantitative relation of forms to each other, and fixes a mutual and invariable interdependence. This _modulus_ is found in the diameter of the column, and the standard of proportion which is based upon it is called a _canon_. In Egypt, as in other countries, there must have been a certain connection between the diameter of a column and its height, but there was no approach to that rigid and immutable law which had its effect upon every detail of a Greek temple. The _modulus_, in Egyptian art, was used with such freedom, and gave rise to such varied proportions, that we may say that no _canon_ existed. The elementary forms of an Egyptian edifice had so little dependence upon the _modulus_ that we need not take it into consideration, and, in this sense, the art of Egypt was not mathematical, like that of Greece. [Illustration: FIG. 67.--The Egyptian Gorge or Cornice.] Finally, all Egyptian buildings are crowned by the same entablature, an architrave and the moulding which is called the Egyptian _gorge_ (Fig. 67).[96] An architectural member, the plain quadrangular architrave, is invariably inserted between this termination and the upper extremity of the voids and points of support. [96] We know but one or two exceptions to this rule. It will suffice to quote the Royal Pavilion of Medinet-Abou, which is crowned by a row of battlements. [Illustration: THE ARAB CHAIN FROM NEAR KENEH] [Illustration: THE PYRAMIDS FROM OLD CAIRO] §3. _General Principles of Construction.--Materials._