Between 850 and 1150 CE, Ancestral Puebloan people constructed an extraordinary complex of multi-story great houses in remote Chaco Canyon, including Pueblo Bonito with its 650 rooms and 40 kivas arranged in a precise D-shape — the largest building in North America for 600 years. Astronomical alignments built into the structures and a road system radiating hundreds of miles across the desert suggest Chaco was a major ceremonial and political center.