1075 A.D. The fifth ruin is a pueblo built of thick, double-coursed masonry. The faces of the stones were smoothed and some retain the peck marks of the tools used in the shaping process. Some of the walls were two stories high. The kiva, located in front of the living rooms, was of excellent construction. The roof was supported on eight stone pillars which rested on the bench, and the walls, from the floor to the top of the pillars, were faced with masonry of good quality. One new architectural feature, the tower, appears in this ruin. There are three of these tall, circular structures—we shall consider them in a moment. The five ruins demonstrate graphically the steady architectural progress of the Developmental Pueblo period. In the beginning the houses were crudely built of posts and adobe and the underground rooms, which may not have been entirely ceremonial at first, were merely deep pitrooms. At the end of the period the houses were of good masonry and the standard Mesa Verde kiva had developed. Certainly this development shows that the people were constantly experimenting and as a result the architecture improved steadily. During the latter part of the period few large pueblos were built. Usually a village consisted of a few living rooms joined together in a compact unit. A short distance south of the living rooms was a single kiva. Pottery also made rapid advances during this period. The women had become convinced of its value and they experimented endlessly, probably in a spirit of friendly competition. During the preceding period pottery was dull gray in color and the crudely painted designs did not contrast well with this drab background. The women now learned to apply a thin wash of white clay to the vessels. This wash or slip, as it is called, produced a clear white background and against this the constantly improving designs stood out in bold contrast. Corrugated pottery appeared and vessels of this type were used chiefly for cooking purposes. Good baskets still were made but pottery vessels were superior to baskets for most purposes. As a result the quality of the baskets began to decline. Sandals were much like those of earlier periods except that the toes were rounded and there was less elaborate decoration. Cotton came into use about the middle of the period and loom-woven cloth made its appearance. Recent experiments have indicated that cotton will not grow in the Mesa Verde so it must have been imported from warmer areas to the south. Minor arts and crafts improved as the people became more proficient in the use of bone, stone and wood. An interesting change occurred in the metate, or milling stone, during this period. Earlier metates were trough-shaped, with a shallow groove for a grinding surface. Now a flat metate came into use and the entire surface was used for grinding the corn.