The same ruin (No. 32) contains an elaborate system of retaining avails, which are shown partly in figure 69. At first a retaining wall was built immediately in front of the main kiva, which is now 5 feet high outside. Apparently this did not serve the purpose intended, for another and much heavier wall was built immediately next to it. This wall is 4 feet thick, flush on top and inside, but 10 feet high outside. At half its height it has a step back of 6 inches. It would seem that even this heavy construction did not suffice, and still another wall was built outside of and next to it. This wall is nearly or quite as heavy as the one described, and its top is on the level of the foot of that wall, but it is 12 feet high outside. Something of the character of the site may be inferred from the arrangement of these walls, which have a combined vertical fall of 27 feet in a horizontal distance of less than 15 feet. The outer or lower wall has a series of very heavy timbers projecting from its face; these are placed irregularly. It should be noted that access to this village was from the bench on either side, and that it could not be reached from the front, where these walls occur. There are other walls on the lower slope, similarly reinforced. A little to the right of the point where these retaining walls occur there is a room in which horizontal beams have been incorporated in the masonry. A similar use of timber occurs in ruin No. 16 and is shown in plate LX. Why timber should be used in this way is not clear. It may be that when the supply was placed on the ground the builders found that they had more timber than was needed for a roof and used the excess in the wall rather than bring up more stone. The posts which were placed vertically and built into the wall were always short; perhaps they were fragments or ends cut from roofing timbers that were found to be too long. In many instances they failed to hold the walls, and possibly the pit holes in sloping rock, which are numerous on some sites, indicate places where this expedient was formerly employed. It is singular that the necessity for such expedients did not develop the idea of a buttress. On this site such an expedient would have saved an immense amount of work. In only one place in the canyon was a buttress found. This was in the Casa Blanca ruin, shown in plate XLVII. There is no doubt that in this place the buttress was used with a full knowledge of its principles, and but little doubt that the idea was imported at a late, perhaps the latest, period in the occupancy of that site. Had it been known before, it would have been used in other places where there was great need for it, not so much to prevent the slipping of walls as to supersede the construction of walls 4 feet thick or more, and to strengthen outside walls which were likely to give way at any time from the outward thrust upon them.