Taken as a whole, the settlements in De Chelly appear to have been well provided with doorways and other openings, and there is no perceptible difference in this respect between the various classes of ruins. Openings were freely left in the walls, wherever convenience dictated, and without regard to the defensive motive, which, in the large valley pueblos, brought about the requirement that all the first-story rooms should be entered from the roof, a requirement which has only recently given way to the greater convenience of an entrance on the ground level. ROOFS, FLOORS, AND TIMBER WORK In the pueblo system of construction roofs and floors are the same; in other words, the roof of one room is the floor of the room above, and where a room or house is but one story high no change in the method of construction is made. The erection of walls was only a question of time, as the unit of the masonry is small; but the construction of a roof was a much harder task, as the beams were necessarily brought from a distance, sometimes a very long distance. The Tusayan claim that some of the timbers used in the construction of the mission buildings, which were established prior to the insurrection of 1680, were brought on the backs of men from San Francisco mountains, a distance of over 100 miles, and references to the transportation of timber over long distances are not uncommon in Pueblo traditions. In De Chelly great difficulty must have been experienced in procuring an adequate supply, as in that portion of the canyon where most of the ruins occur no suitable trees grow. Doubtless in many cases, where the location, under overhanging cliffs permitted, roofs were dispensed with, but this alone would not account for the dearth of timber found in the ruins. If we suppose the canyon to have been the scene of a number of occupancies instead of one, the absence of timber work, as well as the much obliterated appearance of some of the ruins, would be explained, for the material would be used more than once, perhaps several times. The Navaho would not use the timber in cliff ruins under any circumstances, and they would rather starve than eat food cooked with it. Many of the cliff outlooks, being occupied only during the farming season and being also fairly well sheltered, were probably roofless.