The earliest archaeological artifacts in Iran, like those excavated at the Kashafrud and Ganj Par sites, attest to a human presence in Iran since the Lower Paleolithic era. Neanderthal artifacts dating back to the Middle Paleolithic period have been found mainly in the Zagros region at sites such as Warwasi and Yafteh Cave. Early agricultural communities began to flourish in Iran at around 8000 BCE,with settlements such as Chogha Bonut, Susa and Chogha Mish developing in the Zagros region.
The emergence of Susa as a city is determined by C14 dating as early as 4395 BCE. There are dozens of pre-historic sites across the Iranian plateau pointing to the existence of ancient cultures and urban settlements in the fourth millennium BCE. During the Bronze age Iran was home to several civilisations such as Elam, Jiroft and Zayandeh Rud civilisations. Elam, the most prominent of these civilisations developed in the southwest of Iran alongside those in Mesopotamia. The development of writing in Elam in fourth millennium BCE paralleled that in Sumer.The Elamite kingdom continued its existence until the emergence of the Median and Achaemenid Empires.
During the second millennium BCE, Proto-Iranian tribes arrived in Iran from the Eurasian steppes, rivaling the native settlers of the country. As these tribes dispersed into the wider area of Greater Iran and beyond, the boundaries of modern Iran were dominated by the Persian, Parthian, and Median tribes. From the late 10th to late 7th centuries BCE, these Iranian peoples, together with the pre Iranian kingdoms, fell under the domination of the Assyrian Empire, based in northern Mesopotamia. Under king Cyaxares, the Medes and Persians entered into an alliance with Nabopolassar of Babylon, as well as the Scythians, Cimmerians, and Arameans, and together they attacked the Assyrian Empire. The civil war ravaged Assyrian Empire between 616 BCE and 605 BCE, thus freeing their respective peoples from three centuries of Assyrian rule. The unification of the Median tribes under a single ruler in 728 BCE led to the creation of a Median empire which, by 612 BCE, controlled the whole of Iran as well as eastern Anatolia.
In 550 BCE, Cyrus the Great from the state of Anshan took over the Median empire, and founded the Achaemenid empire by unifying other city states. The conquest of Media was a result of what is called the Persian revolt; the brouhaha was initially triggered by the actions of the Median ruler Astyages and quickly spread to other provinces as they allied with the Persians. Later conquests under Cyrus and his successors expanded the empire to include Lydia, Babylon, Egypt, and the lands to the west of the Indus and Oxus rivers. Conflict on the western borders began with the famous Greco-Persian Wars which continued through the first half of the 5th century BCE and ended with the Persian withdrawal from all of their European territories. The empire had a centralised, bureaucratic administration under the Emperor and a large professional army and civil services, inspiring similar developments in later empires.
Achaemenid Empire around the time of Darius the Great and Xerxes.
In 334 BCE, Alexander the Great invaded the Achaemenid Empire, defeating the last Achaemenid Emperor Darius III at the Battle of Issus in 333 BCE. Following the premature death of Alexander, Iran came under the control of Hellenistic Seleucid Empire. In the middle of the 2nd century BCE, the Parthian Empire rose to become the main power in Iran and continued as a feudal monarchy for nearly five centuries until 224 CE, when it was succeeded by the Sassanid Empire. The Sassanids established an empire roughly within the frontiers achieved by the Achaemenids, with the capital at Ctesiphon.Most of the period of the Parthian and Sassanid Empires were overshadowed by the Roman-Persian Wars, which raged on their western borders for over 700 years. These wars exhausted both Romans and Sassanids, which arguably led to the defeat of both at the hands of the invading Muslim Arabs.