The apparent inaccessibility of many of the sites disappears on close examination, and we must not forget that places really difficult of access to us would not necessarily be so regarded by a people accustomed to that manner of life. Many locations which could not be surpassed as defensive sites were not occupied, while others much inferior in this respect were built upon. It was very seldom that the natural conditions were modified, even to the extent of selecting a route of access other than that which, would naturally be followed, and, of course, the easiest route for the cliff dwellers would be also the easiest route for their enemies. In many cases the easiest way of access, which was the one used by the cliff dwellers, was not direct. It was not commanded by the immediate site of the dwellings, except in its upper part, and in some cases not at all. Enemies could climb to the very doors of the houses before they could be seen or attacked. The absence of military knowledge and skill, and of any attempt to fortify or strengthen a site, or even to fully utilize its natural defensive advantages, is characteristic of the cliff ruins of De Chelly. If the cliff dwellers were driven to the use of such places by a necessity for defense, this absence is remarkable, especially as there is evidence that the settlements were occupied for a number of, perhaps a great many, years. Under the head of constructive expedients we have a different result. The difficulties which came from the occupancy of exceptional sites were promptly reflected in the construction, and unusual ways and methods were adopted to overcome them. These methods are the more interesting in that they were not always successful. It sometimes happened that walls had to be placed on a foundation of smooth, sloping rock. In such cases the rock was never cut away, but timbers were employed to hold the wall in place. In some instances the timbers were laid at right angles to the line of front wall, at points where cross walls joined it inside. The front wall thus rested partly on the ends of timbers and partly on rock, while the other ends of the timbers were held in place by the cross walls built upon them. An example of this construction is shown in plate LII. In other instances, where the surface was irregular but did not slope much, timbers were laid on the wall lines and the masonry rested partly upon them. An example of this occurs in the Casa Blanca ruin, shown in plate XLVII. Still another method of using timber in masonry occurs in a number of ruins. It was seldom effective and apparently was confined to this region. This consists of the incorporation into the masonry of upright logs. Figure 69 shows an example that occurs at the point marked 32 on the map. The site here is an especially difficult one, as the builders were compelled to place walls not only on sloping rock foundations, but also on loose debris, and the vertical timber support is quite common.