In studying a natural architecture and in attempting to assign reasons for its particular characteristics, many circumstances have to be taken into consideration. The innate genius of the race, the physical and moral conditions of its development, the perfection of its civilization, the spirit of its religion, and the ardour of its faith; none of these must be forgotten, but some of them act in such a complex fashion that they are extremely difficult to follow. In its aspirations towards the infinite and the eternal, the Egyptian religion raised from the surface of the earth many buildings which varied as greatly in form and aspect as they did in date and situation. The climatic conditions of the world have changed but little since the beginning of the historic period, and every nation has to take them into the first consideration in deciding upon its own architectural forms and principles. We have here a problem whose data do not vary, and yet its solutions have not always been the same even in a single country. Without ever being absolutely incorrect, they attached themselves now to one principle, now to another, and so gave much variety to the appearance of successive buildings under one sky and destined for similar uses. As for the materials employed, we cannot go so far as to say that their different properties absolutely determined the characteristics of Egyptian building in advance. Stone, the chief of all materials, can lend itself to forms of great variety in principle; and so, too, can brick and wood. But although no material can narrowly confine a skilful architect, there are, nevertheless, certain systems and constructions which are only possible with those which possess certain properties.