It is certain that in the early 1st millennium BC, Indo-Iranian nomads began to settle in the western and northwestern Iran. It was at that time that they intermingled with native Iranians.
The first mention of the Medes Civilizations in Assyrian records associates them with the Scythians with whom they shared tribal names, suggesting a certain link between the two tribes. The borders of their lands were never demarked, but it was in an area which is currently northwestern Iran; bordering Mesopotamia to the east, stretching south to the Persian Gulf (Elam, Parthian) and Caspian Sea and the Caucasus to the north.
Assyrian reliance on the Silk Road trade zone made Medes a target for empire building and military diplomacy. Records tell us that Median tribes paid tribute to their powerful neighbors, but were never completely conquered by them. It is likely that it was this aggression that served to unite the Median tribes, creating a formidable military power that in turn began to threaten the Assyrian lands.
The writings of the 5th century Greek historian ’Herodotus’ mentions four kings named Deioces, Phraortes, Cyaxeres and Astyages who ruled a united Medes from the beginning of the 7th century BC to the middle of the 5th century BC.
What is certain is that during the reign of Cyaxares, Medes had developed from being a loose confederation of tribal groupings into a nation under a single king who exacted tribute from Persians, Armenians, Parthians and Aryans.
Cyaxares defeated the Assyrian Empire badly by destroying their religious capital, Ashur in 614 BC. Two years later, while allied with Babylon, the Assyrian capital Nineveh also fell to the Medes.
The Median Empire was at its zenith at that time, encompassing Armenia, Assyria and Cappadocia (now Eastern Turkey) in the west and stretching as far as the Oxus River in the east.
However, Astyages, the son of Cyaxares, was to be the last of the Median kings. In response to the growing power of a coalition of tribes under the leadership of King Cyrus of Anshan, Astyages sent an army to Persia (modern-day Fars province). After brief skirmishes, the army deserted their king, captured him and handed him over to Cyrus in 550 BC.