The siege of Eretria took place in 490 BC, during the first Persian invasion of Greece. The city of Eretria, on Euboea, was besieged by a strong Persian force under the command of Datis and Artaphernes.
The first Persian invasion was a response to Greek involvement in the Ionian Revolt, when the Eretrians and Athenians had sent a force to support the cities of Ionia in their attempt to overthrow Persian rule. The Eretrian and Athenian force had succeeded in capturing and burning Sardis (the regional capital of Persia), but was then forced to retreat with heavy losses. In response to this raid, the Persian king Darius I swore to have revenge on Athens and Eretria.
Once the Ionian revolt was finally crushed by the Persian victory at the Battle of Lade, Darius began to plan to subjugate Greece. In 490 BC, he sent a naval task force under Datis and Artaphernes across the Aegean to subjugate the Cyclades, and then to make punitive attacks on Athens and Eretria. Reaching Euboea in mid-summer after a successful campaign in the Aegean, the Persians proceeded to put Eretria under siege. The siege lasted six days before a fifth column of Eretrian nobles betrayed the city to the Persians. The city was plundered, and the population was deported to the village Ardericca in Susiana near the Persian capital.
After Eretria, the Persian force sailed for Athens, landing at the bay of Marathon. An Athenian army marched to meet them, and won a famous victory at the Battle of Marathon, thereby ending the first Persian invasion.
Background
The first Persian invasion of Greece had its immediate roots in the Ionian Revolt, the earliest phase of the Greco-Persian Wars. However, it was also the result of the longer-term interaction between the Greeks and Persians. In 500 BC the Persian Empire was still relatively young and highly expansionistic, but prone to revolts amongst its subject peoples. Moreover, the Persian king Darius was a usurper, and had spent considerable time extinguishing revolts against his rule. Even before the Ionian Revolt, Darius had begun to expand the Empire into Europe, subjugating Thrace, and forcing Macedon to become a vassal of Persia. Attempts at further expansion into the politically fractious world of Ancient Greece may have been inevitable. However, the Ionian Revolt had directly threatened the integrity of the Persian empire, and the states of mainland Greece remained a potential menace to its future stability. Darius thus resolved to subjugate and pacify Greece and the Aegean, and to punish those involved in the Ionian Revolt.
The Ionian revolt had begun with an unsuccessful expedition against Naxos, a joint venture between the Persian satrap Artaphernes and the Miletus tyrant Aristagoras. In the aftermath, Artaphernes decided to remove Aristagoras from power, but before he could do so, Aristagoras abdicated, and declared Miletus a democracy. The other Ionian cities followed suit, ejecting their Persian-appointed tyrants, and declaring themselves democracies. Artistagoras then appealed to the states of Mainland Greece for support, but only Athens and Eretria offered to send troops.
The reasons that Eretria sent assistance to the Ionians are not completely clear. Possibly commercial reasons were a factor; Eretria was a mercantile city, whose trade was threatened by Persian dominance of the Aegean. Herodotus suggests that the Eretrians supported the revolt in order to repay the support the Milesians had given Eretria in a past war against Chalcis.
The Athenians and Eretrians sent a task force of 25 triremes to Asia Minor to aid the revolt. Whilst there, the Greek army surprised and outmaneuvered Artaphernes, marching to Sardis and there burning the lower city. However, this was as much as the Greeks achieved, and they were then pursued back to the coast by Persian horsemen, losing many men in the process. Despite the fact their actions were ultimately fruitless, the Eretrians and in particular the Athenians had earned Darius's lasting enmity, and he vowed to punish both cities. The Persian naval victory at the Battle of Lade (494 BC) all but ended the Ionian Revolt, and by 493 BC, the last hold-outs were vanquished by the Persian fleet. The revolt was used as an opportunity by Darius to extend the empire's border to the islands of the East Aegean and the Propontis, which had not been part of the Persian dominions before. The completion of the pacification of Ionia allowed the Persians to begin planning their next moves; to extinguish the threat to the empire from Greece, and to punish Athens and Eretria.