The oldest evidence of humankind in Iran Plateau has been unearthed in Kashafrud River region in Khorasan province dating back to 800 thousand years ago.
Historic Iran era dates back to 2500 years ago i.e. the time of the Achaemenid dynasty followed by Seleucid, Parthian, and Sassanid dynasties.
It is a period of time began with the Arabs’ invasion of the country in 642 B.C. and the Iranians gradually converted to Islam; the period which has been continuing up to the present.