Chaco Canyon

36.0544°N, 107.9558°W.

Ancestral Puebloan ceremonial complex in northwestern New Mexico, occupied from approximately 850 to 1150 CE at its peak. Pueblo Bonito, the largest of fifteen great houses, contained over 600 rooms in five stories arranged in a D-shape covering 0.8 hectares. The Chacoan road network extends over 400 km in straight lines across the high desert, climbing cliffs by stairways rather than detouring. Sun Dagger on Fajada Butte uses three sandstone slabs to admit precise daggers of light onto a spiral petroglyph at the summer and winter solstices and equinoxes, and tracks the 18.6-year lunar standstill. Chaco was abandoned by 1150 CE during a multi-decade drought; the population dispersed across the Colorado Plateau. The 2003 Chaco Stratigraphy Project showed that timbers used in great-house construction were transported from forests over 75 km away — 200,000 trees moved without wheels or pack animals.

They built a road system that goes through cliffs instead of around them — and we still cannot explain why the roads are straight.