The trouble began far to the east. When the Greek cities of Ionia rebelled against Persian rule, only two states on the mainland sent help: Athens and Eretria. Why Eretria joined is not entirely clear, though as a trading city its prosperity depended on a free Aegean, and Persian dominance threatened that. The combined Greek force marched inland and burned the lower city of Sardis, the regional Persian capital. It was a fleeting success; Persian horsemen cut them to pieces on the retreat. But the damage to Persian pride was lasting. King Darius I, the histories say, swore revenge on Athens and Eretria, and reportedly ordered a servant to repeat at every meal: "Master, remember the Athenians." The Eretrians were not forgotten either.

In 490 BC the reckoning came. Darius dispatched a naval task force under the admiral Datis and his nephew Artaphernes, with orders to subdue the Cycladic islands and then punish the two cities that had aided the rebels. The fleet hopped westward across the Aegean, took Naxos, and arrived off Euboea in midsummer. The Eretrians, watching the sails gather, sent to Athens for help. Four thousand Athenian settlers came as far as the island, but a leading Eretrian named Aeschines warned them that the city was hopelessly divided and told them to save themselves. They did. Behind the walls, three factions argued: some wanted to surrender for profit, some to flee into the hills, some to fight. As Herodotus put it, "all the plans of the Eretrians were unsound."

The Eretrians chose, finally, to stand behind their walls and endure a siege. It was not a foolish hope. The Persians had come by ship and carried little heavy siege equipment; earlier in the campaign they had been beaten back from the walls of Lindos. For five days the assaults broke against Eretrian defenses and the dead piled up on both sides. On the sixth day the walls were undone not by engines but by treachery. Two prominent men, Euphorbus and Philagros, opened the gates to the enemy. What followed was not a battle but a sack. The temples were looted and burned, an answer to the burning of Sardis, and the city that had stood for centuries was finished in an afternoon.

The survivors were not killed. They were taken. Datis loaded the captured Eretrians aboard ship, left them briefly on the islet of Aegilia, and after the campaign carried them across the sea to the Persian heartland. Brought before Darius at Susa, they were spared his anger and resettled far inland at a village called Ardericca, near a spring that yielded bitumen, salt, and oil. There the exiles stayed. Herodotus, writing decades later, recorded that the Eretrians still lived in Ardericca in his own time, holding onto their old Greek language a thousand miles from the sea that had once made them rich. They were among the first Europeans deported wholesale into Asia, an entire community uprooted and made to begin again as strangers.

From Eretria the Persian fleet sailed south and landed at the bay of Marathon, expecting to repeat the lesson on Athens. The Athenians marched out to meet them and, against the odds, won the victory that has echoed ever since. The first Persian invasion ended there, on the plain of Marathon, but the war did not. Darius died planning a greater army; his son Xerxes finished the work, and a decade later the Persians returned through the pass of Thermopylae. Eretria itself was eventually resettled, and its ruins still lie along the Euboean shore. But the city deported in 490 BC never truly came home.