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

Updated August 2026. There was a trend a few years ago where women asked men how often they thought about the Roman Empire. I rarely do. I think about the Persian Empire instead.

Partly that’s because I’m Persian. “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 are not interchangeable.

This is a conversational history rather than an academic one. I have rewritten it because the old version compressed several centuries too aggressively and repeated a few popular claims that do not survive much scrutiny.

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 is 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.

The old version of this article said Greek rule over Persia lasted only about fifty years. That was too neat. Seleucid power in Iranian lands weakened unevenly. Bactria and Parthia broke away during the third century BCE, but Seleucid authority or suzerainty survived in parts of western and southwestern Iran much longer. Encyclopaedia Iranica describes a long shift from direct rule to local and vassal kingdoms rather than one clean date when “the Greeks left”.

Greek-speaking settlers and cities left a visible mark, especially in urban centres. Iranian elites and local institutions also continued. This was a Hellenistic empire governing a region that remained culturally diverse, not a simple replacement of Persian society by Greek society.

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.

This distinction matters. Calling the Parthians simply “Persians” hides the diversity of ancient Iran. They were an Iranian dynasty ruling Persia, Mesopotamia and many other regions, but they were not just a restored Achaemenid Persian royal house.

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. The old idea that the Parthian period was an awkward intermission between “real” Persian empires is not how historians treat it now. The Arsacid state was one of the major powers of the ancient Near East.

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 is not an Abrahamic religion, as the previous version of this article incorrectly said. It is an Iranian religion centred on Ahura Mazda and associated with the prophet Zarathustra, or Zoroaster.

Exactly when Zoroaster lived is still debated. Scholars have proposed dates from around the second millennium BCE to the sixth century BCE; there is no defensible single date I can drop into a casual paragraph as settled fact.

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.

That ended Sasanian political rule, but it did not mean Iranians instantly became Arabic-speaking Muslims. Conversion was gradual. Research summarised by Encyclopaedia Iranica suggests limited conversion through much of the Umayyad period, followed by faster conversion after the Abbasid revolution; by around the tenth century, Iran had become predominantly Muslim.

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. The result was not the disappearance of Persian culture but the growth of a Persianate Islamic culture that would influence 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 two-thousand-year story 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.