中文摘要：

在2005年野外实地考察过程中,于内蒙古自治区准格尔旗十二连城、神木县大保当古城、鄂托克前旗巴彦呼日呼等古城址城墙中发现“夯层沙”.实验分析表明其成因皆为风成,堆积时代应在建城之前,反映当时地表流动沙丘或半固定、固定沙丘的广泛分布,由此证明鄂尔多斯地区的沙漠在人类大规模开发之前即已存在.这一重要发现为研究本区土地退化、沙漠化等问题提供了新的依据,对西部大开发战略重点之一的生态环境保护与建设具有特殊的历史借鉴意义.

英文摘要：

In 2005, when studying the process of historic sandy desertification on Erdos Plateau, we found that a lot of ancient city ramparts were fortified by alternate layers of sand and soil, and these cities included Shi＇er Lian Ancient City （located in Zungar Banner, Inner Mongolia, China）, Dabaodang Ancient City （located in Shenmu county, Shaanxi province, China）, Bayanhurihu Ancient City （located in Otog Front Banner, Inner Mongolia, China） and so on. They are located in deep desert now. Several researchers have thought that the fate of these ancient cities is associated with natural environmental conditions. However, our experimental result does not support this view. The discovery sheds new light into when and how sandy desertification occurred and provides new historic insight for eco-environment conservation in this district. Through the experiment, some conclusions are drawn as follows： （1） The sandy layer in the ramparts consisting of aeolian-sand which should deposit before the cities were built. Considering the time when these cities were built, we could conclude that the desert scene had existed before the Han Dynasty. Some researchers pointed out that the existence of these cities were associated with good natural conditions when they were built, while our experimental result did not support this view. Accordingly, the existence of these cities could not be an evidence to prove good environmental conditions on Erdos Plateau in historical times. （2） It is an effective way to analyze the environmental change and process of man-land relationship through the fate of the ancient cities, relics, traces of human activities and changes in wasteland reclamation. However, it is not accurate to quantify the time when sandy desertification occurred through the time when these relics were abandoned. Undoubtedly, farming activities in historical times to a certain extent destroyed vegetation on Erdos Plateau, thereby accelerating the process of sandy desertification, but it is not the main factor