The Persian Empire: A Brief History From Cyrus to the Sasanians

Every day, I think about the Persian Empire. Well… not really, but I sometimes do, especially when anyone says anything about Rome. I’m so sick of Rome!

I think about the Persian Empire partly because I’m Persian, and partly because its history runs through so much of western and central Asia. But the name covers several states, separated by centuries.

“Persian” describes an ethnic and cultural identity; “Iranian” is a nationality and a broader identity that includes many peoples. And “Persia” is an old Western name for the country now officially called Iran. Those words overlap, but they aren’t interchangeable.

This is a conversational introduction to the Achaemenids, Seleucids, Parthians and Sasanians, with links to historical research where the dates or claims need a closer look.

On this page

• The Achaemenid Empire: Cyrus to Alexander (c. 550–330 BCE)
• Alexander and the Seleucids: a Hellenistic Iran
• The Parthian or Arsacid Empire (c. 247 BCE–224 CE)
• The Sasanian Empire (224–651 CE)
• The Arab conquest and the end of the last pre-Islamic Persian empire
• So what does “Persian Empire” mean?

The Achaemenid Empire: Cyrus to Alexander (c. 550–330 BCE)

The first empire most people mean when they say “the Persian Empire” is the Achaemenid Empire. Cyrus II, better known as Cyrus the Great, built it in the sixth century BCE by defeating the Medes, taking Lydia in Anatolia and then capturing Babylon in 539 BCE.

Cyrus is remembered unusually well for an ancient conqueror. The British Museum’s Cyrus Cylinder records his takeover of Babylon and restoration of displaced cult statues and religious practices. It’s sometimes marketed as the first declaration of human rights. The British Museum is much more careful: the cylinder is a Babylonian royal inscription, and the modern concept of human rights would have been foreign to its audience.

The empire became larger and more organised under Darius I. It stretched from the Aegean and Egypt across Mesopotamia and the Iranian plateau toward Central and South Asia. Darius divided rule among provinces governed by satraps, developed roads and royal communications, minted imperial coinage and used several languages across administration. Imperial Aramaic became a major bureaucratic and diplomatic language, alongside Old Persian, Elamite, Babylonian and local languages.

The Achaemenids fought several famous wars with Greek states. Xerxes I invaded Greece in 480 BCE, but the campaign failed after Persian victories and defeats that included Thermopylae, Salamis and Plataea. The story is more complicated than “the Spartans beat Persia”; the Greek coalition fought on land and sea, while the Persian Empire remained a major power for another century and a half.

Alexander III of Macedon invaded the empire in 334 BCE. After victories at Granicus, Issus and Gaugamela, he took the Achaemenid capitals and defeated Darius III. By about 330 BCE, Achaemenid rule was over.

Alexander and the Seleucids: a Hellenistic Iran

Alexander died in 323 BCE without a stable succession plan. His generals divided his empire, and Seleucus I eventually built the Seleucid Empire, founded in 312/311 BCE.

Seleucid power in Iranian lands weakened unevenly. Bactria and Parthia broke away during the third century BCE, while Seleucid authority or suzerainty survived in parts of western and southwestern Iran longer. Encyclopaedia Iranica describes a gradual shift from direct rule to local and vassal kingdoms.

Greek-speaking settlers and cities left a visible mark, especially in urban centres. Iranian elites and local institutions also continued. The Seleucids governed a culturally diverse region whose inhabitants kept many local traditions.

The Parthian or Arsacid Empire (c. 247 BCE–224 CE)

The next great Iranian dynasty was the Arsacid dynasty, usually called the Parthians. Their origins are debated in the ancient sources, but the ruling group is generally associated with the Parni, an Iranian-speaking nomadic people who entered Parthia in northeastern Iran. They adopted the name and culture of Parthia and gradually displaced Seleucid control.

The Parthians were an Iranian dynasty ruling Persia, Mesopotamia and other regions. Their name reflects the diversity of ancient Iran: the Arsacid ruling house had different origins from the Achaemenids.

By the reign of Mithridates I in the second century BCE, Arsacid rule extended across much of Iran and Mesopotamia. The Parthians became Rome’s major eastern rival and held power for almost five centuries. Their empire was less centralised than the Achaemenid state, with powerful regional rulers and noble families. That flexibility sometimes looked messy, but it also helped the dynasty survive repeated wars and succession struggles.

Parthian culture mixed Iranian and Hellenistic elements. Greek stayed important on coins and in some cities, while Parthian and other Iranian languages grew in prestige. Encyclopaedia Iranica’s history of the Arsacids describes a state that shaped the ancient Near East for almost five centuries.

The Sasanian Empire (224–651 CE)

In 224 CE, Ardashir I defeated the Arsacid king Artabanus IV and founded the Sasanian Empire. The Sasanians came from Persis/Fars in southern Iran and presented themselves much more explicitly as a Persian imperial dynasty.

The Sasanian state became Rome’s, and later Byzantium’s, great rival in western Asia. Its rulers fought over Armenia, Mesopotamia and the Caucasus, traded across Central and South Asia, and built an imperial culture whose influence continued long after the dynasty disappeared.

Zoroastrianism under the Sasanians

Zoroastrianism was closely tied to Sasanian kingship and developed a stronger organised clergy and canon in this period. It’s an Iranian religion centred on Ahura Mazda and associated with the prophet Zarathustra, or Zoroaster.

Exactly when Zoroaster lived is still debated. Encyclopaedia Iranica’s survey discusses proposals between the middle of the second millennium BCE and the early sixth century BCE. The surviving evidence doesn’t establish a single agreed date.

The Sasanian Empire was also religiously diverse. Jews, Christians and Manichaeans lived across it, and the state’s treatment of minorities varied by ruler and political circumstances. Zoroastrian institutions had strong state support, but describing the whole empire as uniformly Zoroastrian misses that complexity.

The Arab conquest and the end of the last pre-Islamic Persian empire

Decades of war with Byzantium badly weakened both empires. After the death of Khosrow II in 628, the Sasanian court went through rapid succession and civil conflict. Arab Muslim armies then defeated major Sasanian forces in the 630s and 640s. Yazdegerd III, the last Sasanian king, died in 651.

Sasanian political rule ended before most Iranians converted to Islam. Historian Elton Daniel’s Encyclopaedia Iranica survey describes limited conversion during much of the Umayyad period and faster conversion after the Abbasid revolution of 750. The evidence points to a Muslim majority by roughly the tenth century, with substantial differences between regions and between towns and rural communities.

Persian also survived. New Persian emerged in the Islamic period written largely in a modified Arabic script and with substantial Arabic vocabulary. It became a major literary and administrative language across Iran, Central Asia and beyond. Persianate Islamic culture grew across this wider region and influenced dynasties far beyond modern Iran.

So what does “Persian Empire” mean?

Usually it means the Achaemenid Empire, especially in school history and popular culture. But people also use the phrase for the Sasanian Empire, and sometimes more loosely for several Iranian dynasties in between.

If you want the cleanest labels, use Achaemenid, Seleucid, Parthian/Arsacid and Sasanian. They describe different states, different ruling houses and different periods. Calling all of them “Persia” makes a story spanning more than a thousand years sound much simpler than it was.

And yes, I still think about the Persian Empire. I just now have to specify which one.

For the modern language and identity behind those labels, see our guides to Persian and Arabic and the Persian learning resources we recommend.