The most important date, perhaps, in the entire history of the city-in any case, the one on which Eretria was suddenly thrust to the forefront of international politics-is 490 BC. In that year a Persian expedition was sent to Greece by King Darios I to punish the allies of the Ionians who launched a rebellion against his authority in 499. The Persians took the city after a six-day siege, only a short time before they were themselves defeated by the Athenians at Marathon (First Persian War). But it is not at all easy to gauge the impact of this event on the city's residents and buildings. While the sanctuaries were certainly burned (without necessarily being completely destroyed), there is no proof that the whole city was razed or reduced to ashes. In addition, the deportation carried out by the victors probably affected only a small part of the population, since many Eretrians were able to find refuge in the mountainous parts of the territory, which remained inaccessible to the invaders. It is nonetheless certain that several hundred Eretrians, including women and children, were taken far away from Greece and finally settled north of Susa (Iran), the capital of the Achaemenid empire, at a place called Arderrika; their presence there is attested until the beginning of the 4th century and even later.
The best evidence that the city had not lost all means of resistance, despite the dramatic blow it sustained, is provided by the fact that the Eretrians courageously participated, both on land and at sea, in the struggle against the invasion of King Xerxes in 480-479 (Second Persian War). Silver coin issues dated just before the middle of the 5th century and until ca. 430-425 BC even attest to a certain prosperity, not to mention the precious objects, especially from Attica, that have been discovered in the Eretrian tombs of the Early Classical period. Moreover, we know the names of a few famous Eretrians of this period, such as the sculptor Philesios, who worked for his compatriots in Olympia, as well as the poet Achaios, the author of tragedies staged in Athens, or the exile Gongylos, the founder of a princely dynasty in Mysia (Asia Minor), under the aegis of the Great King.