The "apartment houses" of masonry built by the Pueblo/Anasazi people of the American Southwest during Pueblo III times or Classic Pueblo located in rock shelters on the sides of canyon walls. These prehistoric houses were built along the sides or under the overhangs of cliffs primarily in the Four Corners area where the states of Arizona New Mexico Colorado and Utah meet. Mesa Verde National Park's Cliff Palace (CO) and Pueblo Bonito (NM) had about 200-800 rooms each. After this period the Pueblo/Anasazi moved farther south and built the pueblo villages that they still inhabit. When the ancestors of the Pueblo/Anasazi people became sedentary and began to cultivate corn they also began to build circular pits as storage bins. When the bins were later reinforced with stone walls and covered with roofs some people began to use the enclosures as houses. Their use of hand-hewn stone building blocks and adobe mortar was unexcelled even in later buildings. Ceilings were built by laying two or more large crossbeams and placing on them a solid line of laths made of smaller branches. The layers were then plastered over with the adobe mixture. Some of the structures were several stories high creating a row of terraces that gives the structure the appearance of a ziggurat (ancient Babylonian temple tower). The rooms were about 10 x 20 feet (3 by 6 meters). Ground-floor rooms were entered by ladder through a hole in the ceiling; rooms on upper floors could be entered both by doorways from adjoining rooms and by a hole in the ceiling. Each community had two or more kivas or ceremonial rooms. The Pueblo/Anasazi began to build these cliff dwellings around 1000 AD. The cliffs offered natural protection against attack and many smaller communities combined to form the large towns in the cliffs. Toward the end of the 13th century the cliff dwellings were deserted by the inhabitants. Two factors were involved: a severe drought between 1272- 1299 and possibly internal turmoil between tribes. Smaller pueblos were created in the south near better water sources.