National Geographic Society

More than 600 cliff dwellings made by the ancestral Pueblo people, also known as the Anasazi, are scattered throughout Mesa Verde National Park in Colorado (shown here).

The Anasazi arrived in the region as early as A.D. 550, building their homes and cultivating crops on the soaring mesa tops. Around 1150, though, they began to move their dwellings to the alcoves within the canyon walls. Most houses were quite small, but a few reached enormous proportions, housing up 250 people.