In the second half of the 7th century BCE, the Median tribes gained their independence and were united by Deioces. In 612 BCE Cyaxares the Great, Deioces' grandson, and the Babylonian king Nabopolassar invaded Assyria and laid siege to and eventually destroyed Nineveh, the Assyrian capital, which led to the fall of the Neo-Assyrian Empire. The Medes are credited with the foundation of Iran as a nation and empire, and established the first Iranian empire, the largest of its day until Cyrus the Great established a unified empire of the Medes and Persians leading to the Achaemenian Empire (c.550–330 BCE).
Cyrus the Great overthrew, in turn, the Medes, Lydians, and Babylonians, creating an empire far larger than Assyria. He was better able, through more benign policies, to reconcile his subjects to Persian rule; and the longevity of his empire was one result. The Persian king, like the Assyrian, was also "King of Kings," xšāyaθiya xšāyaθiyānām (shāhanshāh in modern Persian) – "great king," Megas Basileus, as known by the Greeks.
Cambyses II conquered Ancient Egypt, overthrowing the Dynasty XXVI. Since he became ill and died before, or while, leaving Egypt, stories developed, as related by Herodotus, that he was struck down for impiety against the Egyptian pantheon. Be that as it may, it led to a succession crisis. The winner, Darius I of Persia, based his claim on membership in a collateral line of the Achaemenid Dynasty.
Darius' first capital was at Susa, and he started the building programme at Persepolis. He rebuilt a canal between the Nile and the Red Sea, a forerunner of the modern Suez Canal. He improved the extensive road system, and it is during his reign that mention is first made of the Royal Road (shown on map), a great highway stretching all the way from Susa to Sardis with posting stations at regular intervals. Major reforms took place under Darius. Coinage, in the form of the daric (gold coin) and the shekel (silver coin) was standardized (coinage had already been invented over a century before in Lydia c. 660 BCE but not standardized), and administrative efficiency was increased.
The Old Persian language appears in royal inscriptions, written in a specially adapted version of cuneiform. Under Cyrus the Great and Darius the Great, the Persian Empire eventually became the largest empire in human history up until that point, ruling and administrating over most of the then known world. Their greatest achievement was the empire itself. The Persian Empire represented the world's first superpower that was based on a model of tolerance and respect for other cultures and religions.
In 499 BCE, Athens lent support to a revolt in Miletus which resulted in the sacking of Sardis. This led to an Achaemenid campaign against Greece known as the Greco-Persian Wars which lasted the first half of the 5th century BCE. During the Greco-Persian wars Persia made some major advantages and razed Athens in 480 BCE, but after a string of Greek victories the Persians were forced to withdraw while losing control of Macedonia, Thrace and Ionia. Fighting ended with the peace of Callias in 449 BCE. In 404 BCE following the death of Darius II Egypt rebelled under Amyrtaeus. Later Egyptian Pharaohs successfully resisted Persian attempts to reconquer Egypt until 343 BCE when Egypt was reconquered by Artaxerxes III.
Hellenic conquest and Seleucid Empire (312 BCE – 63 BCE)Alexander the Great, also known in the Zoroastrian Arda Wiraz Nâmag as "the accursed Alexander", defeated Darius III in the battles of Granicus, Issus and Gaugamela, swiftly conquering the Persian Empire by 331 BCE. Alexander's empire broke up shortly after his death, and Alexander's general, Seleucus I Nicator, tried to take control of Persia, Mesopotamia, and later Syria and Asia Minor.
His ruling family is known as the Seleucid Dynasty. He was killed in 281 BCE by Ptolemy Keraunos. Greek language, philosophy, and art came with the colonists. During the Seleucid Dynasty throughout Alexander's former empire, Greek became the common tongue of diplomacy and literature.
Overland trade brought about some fascinating cultural exchanges. Buddhism came in from India, while Zoroastrianism travelled west to influence Judaism. Incredible statues of the Buddha in classical Greek styles have been found in Persia and Afghanistan, illustrating the mix of cultures that occurred around this time (See Greco-Buddhism).
Parthian Empire (248 BCE – 224 CE)Parthian Empire was the realm of the Arsacid dynasty (اشکانیان), who reunited and governed the Iranian plateau after conquering Parthia and defeating the Greek Seleucid Empire (سلوکیان) in the later 3rd century BCE, and intermittently controlled Mesopotamia between ca 150 BCE and 224 CE.
Parthia was the Eastern arch-enemy of the Roman Empire; and it limited Rome's expansion beyond Cappadocia (central Anatolia). The Parthian armies included two types of cavalry: the heavily armed and armoured cataphracts and lightly armed but highly mobile mounted archers.
For the Romans, who relied on heavy infantry, the Parthians were too hard to defeat, as both types of cavalry were much faster and more mobile than foot soldiers. On the other hand, the Parthians found it difficult to occupy conquered areas as they were unskilled in siege warfare. Because of these weaknesses, neither the Romans nor the Parthians were able completely to annex each other's territory.
The Parthian empire subsisted for five centuries, longer than most Eastern Empires. The end of this empire came at last in 224 CE, when the empire's organization had loosened and the last king was defeated by one of the empire's vassal peoples, the Persians under the Sassanian dynasty.
Sassanid Empire (224 – 651 CE)Ardashir I, started reforming the country both economically and militarily. The empire's territory encompassed all of today's Iran, Iraq, Israel, Lebanon, Jordan, Armenia, parts of Afghanistan, Turkey, Syria, parts of Pakistan, Caucasia, Central Asia, Arabia, and parts of Egypt.
The Persians defeated the Romans in the Battle of Edessa in 260 and took the Roman emperor, Valerian, prisoner for the remainder of his life.
During Khosrau II's rule in 590–628, Egypt, Jordan, Palestine and Lebanon were also annexed to the Empire. The Sassanians called their empire Erânshahr (or Iranshahr, "Dominion of the Aryans", i.e. of Iranians).
A chapter of Iran's history followed after roughly six hundred years of conflict with the Roman Empire. During this time, the Sassanian and Romano-Byzantine armies clashed for influence in Mesopotamia, Armenia and the Levant. Under Justinian I, the war came to an uneasy peace with payment of tribute to the Sassanians.
However the Sassanians used the deposition of the Byzantine Emperor Maurice as a casus belli to attack the Empire. After many gains, the Sassanians were defeated at Issus, Constantinople and finally Nineveh, resulting in peace. With the conclusion of the Roman-Persian wars, the war-exhausted Persians lost the Battle of al-Qâdisiyah (632) in Hilla, (present day Iraq) to the invading forces of Islam.
The Sassanian era, encompassing the length of the Late Antiquity period, is considered to be one of the most important and influential historical periods in Iran, and had a major impact on the world. In many ways the Sassanian period witnessed the highest achievement of Persian civilization, and constitutes the last great Iranian Empire before the adoption of Islam. Persia influenced Roman civilization considerably during Sassanian times, their cultural influence extending far beyond the empire's territorial borders, reaching as far as Western Europe, Africa, China and India and also playing a prominent role in the formation of both European and Asiatic medieval art.
This influence carried forward to the Islamic world. The dynasty's unique and aristocratic culture transformed the Islamic conquest and destruction of Iran into a Persian Renaissance. Much of what later became known as Islamic culture, architecture, writing and other contributions to civilization, were taken from the Sassanian Persians into the broader Muslim world.