The Median Kingdom.
The first kingdom, which was a federation of tribes, created by the Iranians, about 700 BC, was that of the Medes in western Iran. The rise of Media was hindered by invasions from north of the Caucasus Mountains, first by a Thracian people called Cimmerians, followed by Iranian nomads called Scythians. About 625 BC a new attempt was made by the Medes under Cyaxares to form a united kingdom, and after defeating the Scythians, the Medes turned against Assyria. An alliance was made between the Babylonians and the Medes, and the allies stormed and destroyed the Assyrian capital, Nineveh, in 612 BC, a date used today by the Kurds, who claim descent from the Medes, to begin their Kurdish era of time reckoning.

The Achaemenids.
The Medes also subdued the Persians and other Iranians on the plateau, but the Median empire lasted only until 549, when the last Median king, Astyages (r. 584-549), was defeated by his Persian vassal Cyrus The Great, who became the heir of the Median king and ruled an even greater empire from 549 to 530 BC. His son Cambyses II, who ruled from 530 to 522, invaded Egypt. Following an interregnum of a year, Dariush I took power by killing the usurper Smerdis and established the Achaemenid empire on a firm basis. He consolidated and further extended Persian conquests (so that the empire stretched from Egypt and Thrace in the west to northwestern India in the east); established the system of satraps (local governors) under firm centralized control; encouraged the spread of Zoroastrianism; and was a great patron of the arts. Darius's son Xerxes I (r. 486-465), after his defeat by the Greeks in the Persian Wars, retired from active government and set a precedent for future kings who were kept in power by the efficient bureaucracy organized by Darius. Constant revolts were put down, but the weakness of the empire was apparent under Artaxerxes I (r. 465-424), Xerxes II (r. 424-423), and Darius II (r. 423-404). Under Artaxerxes II (r. 404-359), the revolt of his brother Cyrus The Youngeralmost cost him his throne. Artaxerxes III (r. 359-338), an able although cruel monarch, saved the empire from disintegration by reconquering the provinces of Phoenicia and Egypt, which had previously regained their independence. Unfortunately for the Achaemenid empire, Artaxerxes III was poisoned, and a puppet Arses ruled for two years. The last prince of the Achaemenid family, Darius III Codomannus, assumed the throne in 336. He was defeated twice by Alexander and was murdered by his own followers in 330.

The Seleucids.
In the fighting among Alexander's successors, the Diadochi, Iran fell to Seleucus I, who created a new era of time reckoning by his march into Babylon in 312 BC. The Seleucids established many Greek settlements in the east, and under them Hellenism mixed with local cultures to form a syncretic civilization in Iran. The Seleucids never controlled all of the Iranian plateau, and the south, present-day Fars province, was ruled by an independent local dynasty with the title frataraka. In the northern province of Azerbaijan, a Persian satrap from the Achaemenid period called Atropates established a local dynasty and gave his name to the province. In the east the Greeks who settled in Bactria established an independent kingdom about 246 BC, and the Parthians declared their independence from Seleucid rule about the same time.

Although the Seleucids were able temporarily to regain the allegiance of both sets of rebels during the reign of Antiochus III (r. 223-187 BC), the Parthians were to emerge as their heirs.

The Parthians.
The Arsacids, rulers of the Parthians, called themselves phil-Hellene on their coins, and they continued using Greek until the end of the dynasty in AD 224. The Parthians were famous as cavalry soldiers with bows and arrows against the Romans, and they lived in a feudal society. The many small courts of the nobility provided the background for the development of the Persian national epic, which is filled with stories about heroes from the Parthian period. Under the Parthians many small kingdoms existed in uneasy allegiance to an Arsacid king of kings. Among the vassal kingdoms ruled by Arsacid princes was Armenia. The Parthians had to fight the Romans in the west and the Sakas, or Scythians, followed by the Kushans in the east. The lack of unity among the Parthian princes aided the rise of the Sassanian dynasty.

The Sassanians.
The Sassanians were not phil-Hellene like their predecessors but sought to establish a national Persian renaissance in both culture and ideology. From the outset Ardashir I, who killed his Parthian overlord in AD 224, proclaimed a revival of ancient glory, although the Sassanians had only the faintest memory of the Achaemenids. The early buildings of Ardashir in Fars province were massive, proclaiming imperial grandeur. The centralization of power in the hands of the king of kings was the opposite of the Parthian period of history. After Shapur I 's victory over the Romans and capture of the Emperor Valerian in 260, he proclaimed his power in a series of rock reliefs in Fars depicting his victories. Roman prisoners were employed in building dams and irrigation projects in various parts of the Sassanian empire. During Shapur's reign Zoroastrianism became the official state religion.

Shapur's successors--his son Hormizd Ardashir (r. 272-73), another son Bahram I (r. 273-76), his grandson Bahram II (r. 276-93), and another son Nerseh (r. 293-302)--all sought to strengthen dynastic power as opposed to the nobility. Under Hormizd II (r. 302-09), SHAPUR II (r. 309-79), Ardashir II (r. 379-83), Shapur III (r. 383-88), and Bahram IV (r. 388-99), wars with Rome alternated with struggles against nomadic invaders from the east. Yazdegird I (r. 399-421) relaxed the persecution against Christians, who had been suspected of having been secret allies of the Romans since Shapur II . Bahram V (r. 421-39) was surnamed Gur because of his skill in hunting the onager. Many stories are told about him in the national epic, Shah Nameh, by Firdawsi and elsewhere. Yazdegird II (r. 439-57), Hormizd III (r. 457-59), Peroz (r. 459-84), and Balash (r. 484-88) had difficulties with the Hephthalites (White Huns) in present-day Afghanistan. Under Kavad (r. 488-531) and his brother Zamasp (r. 496-98), a communistic socioreligious movement led by the "prophet" Mazdak gained adherents. It was savagely suppressed by Khosru I (r. 531-79), who has been called the greatest ruler of the dynasty. Hormizd IV (r. 579-90) was followed by Bahram Chobin (r. 590-91), the only successful rebel against the Sassanian house. He was overthrown by Khosru II (r. 591-628), the last great Sassanian ruler. Khosru II tried to reestablish the frontiers of the Achaemenid empire, but initial success was followed by defeat at the hands of the Byzantine emperor HERACLIUSand assassination. A succession of rulers culminated in Yazdegird III (r. 632-51), under whom the exhausted Sassanian empire succumbed to the attacks of the Muslim Arabs.