The ancient nation of Iran was historically known to the West as Persia until March 21 , 1935 (see also History of Persia , History of Levant ). Once a major empire in its own right, it has been overrun frequently and has had its territory altered throughout the centuries. Invaded by Arabs , Seljuk Turks , Mongols , and others--and often caught up in the affairs of larger powers--Iran has always reasserted its national identity and has developed as a distinct political and cultural entity.
Archeological findings have placed knowledge of Iranian prehistory at middle paleolithic times (100,000 years ago). The earliest sedentary cultures date from 18,000-14,000 years ago. The sixth millennium BC saw a fairly sophisticated agricultural society and proto-urban population centers. Many dynasties have ruled Iran, the first of which was under the Achaemenids (559 - 330 BC), a dynasty founded by Cyrus the Great . After the Hellenistic period (300 - 250 BC) came the Parthian (250 BC - AD 226 ) and the Sassanid (226 - 651) dynasties.