In ancient times, and even today, water resources, especially rivers, were the main reasons for the existence of human settlements and the formation of the idea of urbanity in the people's minds. This phenomenon can be seen in all places where ancient civilizations were established, e.g. in Egypt, Mesopotamia, Transoxiana and Sind due to the rivers Nile, Tigries and Euphrates, Amu Darya and Syr Darya and Sind, respectively. The Helmand civilization, therefore, was not an exception. Furthermore, after passing a long distance through a desert, the Helmand River reaches the Sistan basin which is a closed inland delta surronded by terribly dry deserts from every side. This special situation makes the Sistan basin and interesting area for attracting human settlements.
The abundance of water in the southern delta of the Helmand River, the oldest one of the two deltas, created a suitable environmental situation for the people during the fourth millennium BC to settle and establish the only large urban centre, i.e. Shahr-i Sokhta, in the eastern part of the Iranian plateau in Sistan. Natural phenomena such as climate change at the end of the third millennium BC, long droughts, change of the river bed because of tectonic phenomena at the level of the continental platform and violent dust storms caused people to abandon the area after a thousand year of flourishing. Some settlements were established in different parts of the southern delta in intervals after the collapse of Shahr-i Sokhta up to the 18th century. However, considering the small amount of water this delta received, an urban settlement like Shahr-i Sokhta was never established again. Even in the southern delta, where the inhabitants of Shahr-i Sokhta might have moved, no such large prehistoric urban settlement was found, perhaps due to constant floods, droughts and the famous Wind of One Hundred and Twenty Days which buried buman settlements and blocked the irrigation canals.
Uppsala: Uppsala University , 2010. 221-241 p.