<P> The city of Eretria also sent assistance to the Ionians for reasons that 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 . </P> <P> The Athenians and Eretrians sent a task force of 25 triremes to Asia Minor . 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 . </P> <P> In the spring of 492 BC an expeditionary force, to be commanded by Darius's son - in - law Mardonius, was assembled, consisting of a fleet and a land army . Whilst the ultimate aim was to punish Athens and Eretria, the expedition also aimed to subdue as many of the Greek cities as possible . Departing from Cilicia, Mardonius sent the army to march to the Hellespont, whilst he travelled with the fleet . He sailed round the coast of Asia Minor to Ionia, where he spent a short time abolishing the tyrannies that ruled the cities of Ionia . Ironically, since the establishment of democracies had been a key factor in the Ionian Revolt, he replaced the tyrannies with democracies . </P> <P> Thence the fleet continued on to the Hellespont, and when all was ready, shipped the land forces across to Europe . The army then marched through Thrace, re-subjugating it, since these lands had already been added to the Persian Empire in 512 BC, during Darius's campaign against the Scythians . Upon reaching Macedon, the Persians forced it to become a fully subordinate part of the Persian Empire; they had been vassals of the Persians since the late 6th century BC, but retained their general autonomy . </P>

The persian empire attacked greece by both land and sea