Recently five ruins dating from this period have been excavated in the Mesa Verde. Two of the ruins are at the Twin Trees site, with one ruin sitting on top of the other. The other three are less than three hundred yards away at Site 16. And here again the ruins are piled up one on top of another. The people showed a strong tendency to build villages on the ruins of earlier villages. The five ruins, taken in chronological order, show very clearly the architectural progress of the Developmental Pueblo period: 850 A.D. The first ruin is a slab-house pueblo. The floors of the living rooms were a foot or more below ground level and the earthen walls were lined with slabs. The upper walls consisted of slender posts, set a few inches apart, with the intervening spaces filled with adobe. In front of the long row of living rooms were four pitrooms, each one being about six feet deep. The roof of each pitroom was supported on four posts set in the floor of the room. 900 A.D. The second ruin is a post-and-adobe pueblo. The floors of the living rooms were not dug below ground level and no stone slabs were used. The walls consisted of posts, set upright a foot or more apart. The spaces between the posts were filled with adobe into which had been forced many small stones. In front of the living rooms was a kiva of a very early type. The walls were of plastered native earth. The roof was supported on four posts but instead of rising from the kiva floor the posts were built into the face of a bench which encircled the room. 950 A.D. The third ruin is a small masonry pueblo. The walls were built of stones and adobe but the masonry was exceedingly crude. The stones were irregular in shape and only a few were laid in even rows. An excessive amount of adobe was used; actually the walls were about fifty percent adobe and fifty percent stone. In front of the living rooms was an early type kiva. The walls were of plastered native earth and the roof, instead of being supported on posts, was supported on four stone pillars, or pilasters, which rested on the bench. 1000 A.D. The fourth ruin is a small pueblo built of single-coursed masonry. The walls of the living rooms contain stones which were well shaped but without smoothed faces. The stones were laid in even rows but the walls were only the thickness of a single stone, measuring less than a foot in width. The kiva, which was located in front of the living rooms, approached the standard Mesa Verde type. The walls below the bench were faced with stone and the roof was supported by six stone pilasters which rested on the bench.