What-if: Xerxes Conquers the Greek City States

Few historical stories have shaped modern imagination quite like the stand at Thermopylae. The image is almost universal at this point: King Leonidas and his 300 Spartans holding a narrow pass against the “endless” Persian army. It’s been retold by ancient writers, romanticized by Enlightenment historians, and immortalized again in modern pop culture, most famously in Frank Miller’s 300 graphic novel and its film adaptations.

It’s a story about defiance against overwhelming force. About freedom against empire. About a small, fractured Greece standing against the greatest empire the world had yet seen. But that raises a question that rarely gets asked in detail—what if things had gone differently?

What if the Persians had broken through? What if Xerxes had succeeded where history says he failed? And more importantly, what would that have meant for the trajectory of Western civilization itself? 

Who was Xerxes, and why did he invade Greece?

Relief associated with Xerxes I, on display at the National Museum of Iran, illustrating the imperial iconography of the Achaemenid Empire and the royal authority of one of antiquity’s most powerful rulers.

Xerxes I ruled the vast Achaemenid Empire at its height, stretching from the Indus Valley to the edges of Europe. When he launched his invasion of Greece in 480 BCE, it was not a reckless conquest but a continuation of a longer imperial struggle. 

Xerxes father, Darius I, had invaded Greece ten years before to punish Athens and Eretria for their support of the revolts in Persian-controlled Ionia. Defeated at the Battle of Marathon, Xerxes sought to rectify this embarrassment and punish the Greeks once and for all. 

What happened to Xerxes’ invasion?

The Greco-Persian Wars are often remembered as a story of heroic resistance culminating in Greek victory. Thermopylae, Salamis, and Plataea form a narrative arc of defiance overcoming empire. But in more practical terms, Persia’s failure culminated in its naval defeats. The ability to protect the pontoon bridge from Helispont and supply this vast military came down to sea power. 

Often misattributed to American World War II General Omar Bradley, a single aphorism reigns true here. Gen. Robert H. Barrow (USMC) in 1980 said: “Amateurs talk tactics, professionals study logistics.” 

The Persian army was massive by ancient standards. While some of the Greek sources have claimed anywhere between 2.5-5 million men, historians generally agree the force was more likely between 100,000-300,000 men, with roughly 70,000-120,000 being actual combat troops, the rest in support or other roles such as sailors. 

The critical vulnerability was not necessarily battlefield performance on land. It was naval coordination and sustained supply support for such a large expeditionary force deep in hostile territory.

Illustration depicting the construction of a massive pontoon bridge across the Hellespont during the Persian invasion of Greece, where Phoenician engineers and sailors assembled floating platforms to enable the passage of King Xerxes I’s army into Europe.

At the Battle of Salamis, the Persian navy was drawn into combat in constrained waters where Greek triremes had the advantage. The resulting loss forced Xerxes to leave his army, hand command to Mardonius, and head back to Persia for fear he might be cut off if the Greeks destroyed their pontoon bridge. It also greatly limited the Persians’ ability to support the land army by sea. 

If Persia had avoided Salamis entirely or won it decisively, the consequences would have been profound. A secure navy would have meant:

• Stable supply lines to the mainland army

• Reduced pressure on Xerxes to withdraw

• Sustained occupation of central and southern Greece

  
  

This could’ve enabled the Persians to maintain the initiative and secure victories elsewhere, both on land and at sea. Assuming that happens, what would a Persian-conquered Greece look like? 

A Conquered Greece does not mean a Peaceful Greece

If Xerxes had succeeded, Greece would not simply become a quiet Persian province. The empire was already experienced in managing diverse and often rebellious territories. Greece would likely have been absorbed into a system of satrapies, locally governed but ultimately controlled by Persian authority.

Map illustrating the major theaters, campaigns, and battles of the Greco-Persian Wars, highlighting the territorial extent of the Achaemenid Empire and the network of Greek city-states involved in resistance during the 5th century BCE.

Some cities would collaborate, but resistance would remain, and it’s safe to say that the potential for rebellions would remain high. Athens, in particular, would remain a symbolic flashpoint, especially given how they would’ve felt especially eager for vengeance, given that Xerxes actually burned Athens to the ground in real life. Even under occupation, Athenians would most likely retain some of their cultural identity and the memory of resistance. 

The Impact of the Persian Conquest on History 

A stable Persian victory in Greece would have dramatically altered the balance of power in the Mediterranean. Without an independent Greek world:

• Macedon would not rise in the same way or perhaps later.

• Alexander the Great would likely never have emerged as a unifier of Greece and conqueror of Persia.

• The Hellenistic world, which spread the Greek language and culture across Egypt and the Near East, would never fully exist or emerge later in some fashion.

  
  

That single absence would ripple through the centuries, shaping the rise of Rome, which would still become a force in the Mediterranean, but in a very different intellectual and cultural environment.

Historically, Rome absorbed Greek philosophy, art, and political theory through conquest and imitation. Greek culture became the foundation of Roman elite education and, later, the Western intellectual tradition. But in a world where Greece is never independent, or is absorbed into a Persian imperial system, that transmission is weakened, delayed, or fundamentally altered.

Rome might still expand, but it would not inherit a fully formed Hellenic intellectual world in the same way. And that changes everything downstream from philosophy and political theory to science, historiography, and even early theological development in the Mediterranean world. 

Could Persian Dominance Last?

 

Even if Xerxes had succeeded, the bigger question would have been the longevity of control and stability. Because the Persian Empire already faced recurring rebellions in its provinces and succession crises stemming from infighting within its political elite. 

Between roughly 465 BCE and 424 BCE, the empire experienced:

• A violent succession crisis after the assassination of Xerxes I

• Widespread provincial revolts (notably in Egypt and Babylon)

• Another major dynastic crisis during the transition to Darius II

  
  

Now imagine a Presian-controlled Greece inside that system. Greece would not be a passive province. It had always been geographically difficult to control and culturally resistant, though that varied from case to case. But one must wonder what would happen during such crises in Greece.  

If Persia was weakened during a succession crisis or a rebellion, rebellious Greeks may seize the opportunity to revolt. Athens would likely serve as the ideological center of resistance, especially due to its historical memory of independence and its naval capacity.

Sparta, by contrast, would be slower and more cautious, joining only when Persia clearly weakened or when Athenian power threatened to dominate Greece again. In practice, Greek resistance would not be a unified moral uprising. It would be a shifting coalition of opportunistic city-states responding to imperial weakness. And they would not be alone.

Egypt had a long history of rebellion under Persian rule, and would likely seize any moment of instability to break away.  Carthage, meanwhile, would view Persian expansion through the lens of trade and maritime influence. It would not need to invade directly to matter; financial and naval support for Greek resistance would be enough to shift the balance of power.

So what actually happens in the long run?

Even in a successful Xerxes scenario, three forces remain constant:

1. Geography – Greece is fragmented and hard to hold

2. Imperial cycles – Persia is strong under kings, fragile in transitions

3. External opportunism – other powers and provinces exploit moments of weakness

   
   

That combination makes long-term stability difficult to maintain. Instead of a permanently conquered Greece, the more realistic outcome is a province with repeated rebellions, cycles of suppression, and perhaps an eventual fragmentation of the Persian empire in this part of the war due to the factors we’ve discussed or other unknowns that might come into play (another invasion by other peoples or some other event.

And in such a world, Greece does not disappear but becomes a contested frontier between empires, where rebellion was just a matter of time. 

Sources 

1. Beard, M. (2015). SPQR: A history of ancient Rome. Liveright Publishing.

2. Boardman, J., Griffin, J., & Murray, O. (Eds.). (2001). The Oxford history of Greece and the Hellenistic world. Oxford University Press.

3. Briant, P. (2002). From Cyrus to Alexander: A history of the Persian Empire. Eisenbrauns.

4. Cartledge, P. (2006). Thermopylae: The battle that changed the world. Oxford University Press.

5. Cartledge, P. (2009). Ancient Greece: A history in eleven cities. Oxford University Press.

6. Goldsworthy, A. (2006). Caesar: Life of a colossus. Yale University Press.

7. Green, P. (1996). The Greco-Persian Wars. University of California Press.

8. Holland, T. (2005). Persian fire: The first world empire and the battle for the West. Doubleday.

9. Hornblower, S. (2011). The Greek world 479–323 BC. Routledge.

10. Kuhrt, A. (2007). The Persian Empire: A corpus of sources from the Achaemenid period. Routledge.

11. Waterfield, R. (2009). Why Socrates died: Dispelling the myths. W. W. Norton.

12. Waters, M. (2014). Ancient Persia: A concise history of the Achaemenid Empire, 550–330 BCE. Cambridge University Press.

images

1. Wikimedia Commons. (n.d.). Battle of Thermopylae - pass.jpg [Photograph]. https://commons.wikimedia.org/wiki/File:Battle_of_Thermopylae_-_pass.jpg

2. Wikimedia Commons. (n.d.). Construction of Xerxes Bridge of boats by Phoenician sailors.jpg [Illustration]. https://commons.wikimedia.org/wiki/File:Construction_of_Xerxes_Bridge_of_boats_by_Phoenician_sailors.jpg

3. Wikimedia Commons. (n.d.). Map Greco-Persian Wars-en.svg [Map]. https://commons.wikimedia.org/wiki/File:Map_Greco-Persian_Wars-en.svg

4. Wikimedia Commons. (n.d.). National Museum of Iran Darafsh (785).JPG [Photograph]. https://commons.wikimedia.org/wiki/File:National_Museum_of_Iran_Darafsh_(785).JPG