The area occupied by the modern country of Iran was home to simple semiagrarian cultures as early as 13,000 b.c. Conditions on the plateau, however, were not well suited for the development of the kind of advanced agricultural societies that appeared in other parts of the Fertile Crescent. Without any great rivers to exploit, that had to await the development, at an uncertain but late date, of a satisfactory method of irrigation, now known as the kariz or qanât system (a network of underground channels to carry water by gravity feed from highland water tables to fi elds at lower elevations). In some areas, agriculture was thus eclipsed by pastoralism (herding cattle, probably on a nomadic basis, to graze on the meager natural vegetation) or by trading societies supplying the great cities of Mesopotamia and the Indus with raw materials such as metal. It was only along the Kârun River in the southwest that geographic factors were conducive to the rise of an early civilization. This area was really just an extension of the Mesopotamian plain and was under the infl uence of Mesopotamian culture, but it came to be occupied by a people, the Elamites, who defi nitely had their roots on the plateau. They formed a kingdom in approximately 2700 b.c. and became a major power during the period 1500–1100 b.c. , when they even managed briefl y to defeat and sack Babylon.
Although the Elamites thus founded the fi rst known civilization in Iran, they were not ethnically “Iranian”: that is, they spoke a unique language that cannot be connected with any other particular group of languages. It was at about the time when their kingdom was at its peak that people calling themselves Aryans (from a word probably meaning “noble”) and speaking languages belonging to the Iranian group moved onto the Iranian plateau. The process of migrations or invasions that separated these Iranians from the closely related Indo-Aryans (who moved into the Indus Valley) and brought them onto the plateau is diffi cult to trace and highly controversial among specialists. It is clear enough, though, that Iranian tribes had reached the Zagros by the beginning of the fi rst millennium b.c. One of these tribal groups, the Medes, was under attack by the Assyrians from 881–788 b.c. In response, the Medes eventually organized themselves into a kingdom with a capital at Ecbatana (modern Hamadân in the central Zagros). Under King Cyaxares (625–584 b.c. ), the Medes allied with Babylon to crush the Assyrians. They subsequently expanded into Asia Minor (modern Turkey), where, after an indecisive war with the Lydians, they negotiated a border along the Halys River.