DAVID ROBERTS / NATURE'S IMAGES / SCIENCE PHOTO LIBRARY DAVID ROBERTS / NATURE'S IMAGES / SCIENCE PHOTO LIBRARY
A portion of Spruce Tree House, Mesa Verde National Park, Colorado, showing remains of a pit house, or kiva. Kivas were used for a variety of purposes and considered ceremonial chambers. Spruce Tree House, the third largest cliff dwelling, was constructed between A.D. 1211 and 1278 by the ancestors of the Puebloan peoples of the Southwest. The dwelling contains about 130 rooms and 8 kivas. Mesa Verde is also a Unesco World Heritage Site.
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