Considering all that has been written about the cliff ruins as defensive structures, it is strange how little direct evidence there is to support the hypothesis; how few examples can be cited which show anything that can be construed as the result of the defensive motive except the general impression produced on the observer. Nor, on the other hand, do these ruins as a whole give any support to the theory that they represent an intermediate stage in the development of the pueblo people. Some few may, perhaps those examined by Mr F. H. Cushing south and east of Zuni do; but more than 99 per cent of them give more support to a theory that they are the ultimate development of pueblo architecture than to the other hypothesis, for they contain in themselves evidence of a knowledge of construction equal and even superior to that shown in many of the modern pueblo villages. The only thing anomalous or distinctive about the cliff ruins, considered as an element of pueblo architecture, is the character of site occupied. If this were dictated by the defensive motive, it would seem reasonable to suppose that the same motive would have some direct influence on the structures, yet examples where it has affected the arrangement of rooms or ground plan or the character of the masonry are exceedingly rare and generally doubtful. It is well to specify that in the preceding remarks the term cliff ruin has been applied to small settlements, comprising generally less than four rooms, sometimes only one or two, and usually located on high and almost inaccessible sites. These are comprised in class IV of the classification here followed. Regular villages located in the cliffs or on top of the talus (class III) are a different matter. These have nothing in common with the small ruins, except that sometimes there is a similarity of site. Doubtless in some of these ruins the defensive motive operated to a certain extent. In classes I and II, however, the influence of the defensive motive, in so far as it affected the character of site chosen, is conspicuous by its absence. As there is no evidence that the cliff ruins of class IV were separate and distinct from the other ruins, but the contrary, the defensive motive may be assigned a very subordinate place among the causes which produced that phase of pueblo architecture found in Canyon de Chelly.