The Anasazi, or Ancestral Pueblans were a Native American people who lived near the "Four Corners" region where Arizona, Utah, Colorado, and New Mexico intersect from about the time of Christ's birth to 1300 AD, when they began to disappear for reasons that are still not clear today.  (Anasazi is a Navajo term meaning "the ancient ones" or "ancient enemies", so the term "Ancestral Pueblans" is preferred by the Pueblo people, and many others </ref> The Anasazi lived as hunter-gatherers for awhile, then began to settle in villages around 490 AD.
The Anasazi were highly influential to Native American architecture. Many lived in circle-shaped pitlike structures with a sipapu - a hole in the ground. Others lived in caves. The former went on to influence the structure of the Pueblo ceremonial room known as the kiva. A kiva always contains a sipapu, and the Pueblo believe is that this is where their ancestors entered the world.  The Anasazi were also known for their horticulture - which was not easy for them, given the arid climate in which they lived - and their pottery. 
A common misconception is that the Anasazi completely disappeared, and this is not quite accurate, as their descendants survive to this day. However, their status as a continuing culture vanished, with only their many influences remaining. 
- Appiah & Gates, The Dictionary of Global Culture, Alfred A. Knopf, New York 1997