Typically, one major town dominated each basin, and there were complex economic relationships between the town and the hundreds of villages that surrounded it. In the higher elevations of the mountains rimming the basins, tribally organized groups practiced transhumance, moving with their herds of sheep and goats between traditionally established summer and winterpastures. There are no major river systems in the country, and historically transportation was by means of caravans that followed routes traversing gaps and passes in the mountains. The mountains also impeded easy access to the Persian Gulf and theCaspian Sea.
With an area of 1,648,000 square kilometres (636,000 sq mi), Iran ranks eighteenth in size among the countries of the world. Iran shares its northern borders with three post-Soviet states: Armenia, Azerbaijan, and Turkmenistan. These borders extend for more than 2,000 kilometres (1,200 mi), including nearly 650 kilometres (400 mi) of water along the southern shore of the Caspian Sea. Iran's western borders are with Turkey in the north and Iraq in the south, terminating at the Arvand Rud.
The Persian Gulf and Gulf of Oman littorals form the entire 1,770 kilometres (1,100 mi) southern border. To the east lieAfghanistan on the north and Pakistan on the far south. Iran's diagonal distance from Azerbaijan in the northwest to Sistan and Baluchestan Province in the southeast is approximately 2,333 kilometres (1,450 mi).
Geographically, Iran is located in West Asia and borders the Caspian Sea, Persian Gulf, and Gulf of Oman. Its mountains have helped to shape both the political and the economic history of the country for several centuries. The mountains enclose several broad basins, or plateaus, on which major agricultural and urban settlements are located. Until the 20th century, when majorhighways and railroads were constructed through the mountains to connect the population centers, these basins tended to be relatively isolated from one another.