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. In 492 BC, once the Ionian Revolt had finally been crushed, Darius dispatched an expedition to Greece under the command of his son-in-law, Mardonius. Mardonius re-conquered Thrace and compelled Alexander I of Macedon to make Macedon a client kingdom to Persia, before the wrecking of his fleet brought a