The general outlines of the development of this architecture wherein the ancient builders were stimulated to the best use of the exceptional materials about them, both by the difficult conditions of their semi-desert environment and by constant necessity for protection against their neighbors, can be traced in its various stages of growth from the primitive conical lodge to its culmination in the large communal village of many-storied terraced buildings which we find to have been in use at the time of the Spanish discovery, and which still survives in Zuñi, perhaps its most striking modern example. Yet the various steps have resulted from a simple and direct use of the material immediately at hand, while methods gradually improved as frequent experiments taught the builders more fully to utilize local facilities. In all cases the material was derived from the nearest available source, and often variations in the quality of the finished work are due to variations in the quality of the stone near by. The results accomplished attest the patient and persistent industry of the ancient builders, but the work does not display great skill in construction or in preparation of material. The same desert environment that furnished such an abundance of material for the ancient builders, also, from its difficult and inhospitable character and the constant variations in the water supply, compelled the frequent employment of this material. This was an important factor in bringing about the attained degree of advancement in the building art. At the present day constant local changes occur in the water sources of these arid table-lands, while the general character of the climate remains unaltered. The distinguishing characteristics of Pueblo architecture may be regarded as the product of a defensive motive and of an arid environment that furnished an abundance of suitable building material, and at the same time the climatic conditions that compelled its frequent employment.