The Great Kiva, Chaco Canyon
Between AD 850 and 1250, Chaco Canyon was a major center of ancestral Puebloan culture. Many diverse clans and peoples helped to create a ceremonial, trade, and administrative center whose architecture, social organization and community life was unlike anything before or since.
Chaco is remarkable for its monumental public and ceremonial buildings and its distinctive architecture. The Chacoan people combined pre-planned architectural designs, astronomical alignments, geometry, landscaping, and engineering to create an ancient urban center of spectacular public architecture. Chaco was connected to over 150 communities throughout the region by engineered roads and a shared vision of the world. After 1250, the people migrated from the area, moving south, east, and west, to join relatives living on the Hopi Mesas, along the Rio Grande, and around Zuni Mountain.
http://www.nps.gov/history/worldheritage/chaco.htm