Mesa Verde National Park， in Colorado， America， has many“cliff dwellings2”， places that are built into cliffs where people once lived. They look almost impossible to get to. Who lived in them， and why did they live there？

People lived there about 800 years ago. Americans call them the Ancestral Puebloans. They grew food on the mesa3， the flat land on top of the cliffs. They kept animals over the mesa to trade with each other. Why didnt they build homes on the mesa？

One reason was the weather. Winters were getting colder and colder. The mesa was flat and open. There was no protection from the cold winds. Most of the cliff dwellings face south or southwest—away from the cold north wind. Another reason people didnt live on the mesa is that there were more and more people to feed. Homes on the mesa would use land that was needed to grow food. Some people say a third reason was for safety. They say different groups of Ancestral Puebloans were fighting each other. The cliff dwellings were hard to get into， so they kept the people who lived there safe. People who study Ancestral Puebloans argue about this reason. Some people dont believe it. They say the groups traded too much to have been fighting.

Everyone agrees that these people were very skilled builders， who used every bit of space in the cliffs to make their homes. Its a really admiring4 thing.

美國科羅拉多州的梅薩維德國家公園有很多懸崖屋，那里曾經(jīng)有人居住過，如今改建成了懸崖。表面上看不可能進得去。那么誰曾住過那里呢？為什么他們會住在那里呢？

有一群人生活在那里大概有800年了。美國人稱他們?yōu)楣偶枕f布洛人。他們在位于懸崖頂處平坦的平頂山上種植食物。他們還在平頂山上飼養(yǎng)動物，互相交易。為什么他們不把房屋建在平頂山上呢？

其一是因為氣候。冬天天氣越來越冷了。平頂山既平坦又空曠。沒有抵御凜冽寒風(fēng)的保護措施。很多懸崖屋為了避開北面的寒流而面朝南方或西南方。人們不居住在那里的另外一個原因是有越來越多的人要養(yǎng)活。平頂山的房屋會占用那些本要用于種植食物的土地。有些人說第三個原因是安全問題。古吉普韋布洛人的各部落之間過去常常發(fā)生斗毆。懸崖屋很難進去，所以他們要確保住在那里的人的人身安全。研究古吉普韋布洛族的人們對于這點卻意見相左。有些人不相信這一點，他們認為部落間交易頻繁，是不會發(fā)生斗毆。

每個人都認為那里的人是技藝高超的工匠，他們能利用懸崖上的每一點空間修建房屋。這點的確讓人嘆服不已。