Some of the most famous of all buildings of this period are those of Mesa Verde,[73][95] whose location in high cliffs has led to the use of the name “Cliff Dwellers” for the people who lived here from the middle of the eleventh century until the latter part of the thirteenth. Mesa Verde is a large plateau in the drainage of the Mancos River in southwestern Colorado. Here in great, high caves, protected by massive sandstone overhangs, but open to the sun, were built huge houses which were really cities. These pueblos were in many essentials like those of Chaco Canyon and other open sites, but they seem to have grown by accretion rather than according to a fixed plan, and the shape of the structures was largely determined by that of the caves which sheltered them. There are certain unmistakable differences between the architecture and pottery of Chaco Canyon and of Mesa Verde. As in the case of the Chaco culture, Mesa Verde traits were not confined to the type locality, but had a far-reaching influence. Numerous ruins with the same basic characteristics, but not necessarily in caves, are found along the Mancos River and for some distance to the east and to the west. After the abandonment of the Mesa Verde proper, the influence became quite important in the south. At Mesa Verde walls were thinner than in the Chacoan houses. This can probably be traced to the material used, as well as to the fact that the cave ceilings somewhat limited the height of the buildings, and with the reduced strain, thick walls were not needed. Flat tabular stones were not available, and walls were constructed of massive stone which was shaped into large, loaflike, blocks by pecking. Walls were of solid rock with no center fill of rubble or earth, and little mortar was used. [Illustration: Fig. 31—Cliff Palace, Mesa Verde National Park, Colorado.]