'The first campaign in 492 BC, led by Mardonius, re-subjugated Thrace and forced Macedon to become a client kingdom of Persia. However, further progress was prevented when Mardonius's fleet was wrecked in a storm off the coast of Mount Athos. The following year, having demonstrated his intentions, Darius sent ambassadors to all parts of Greece, demanding their submission. He received it from almost all of them, excepting Athens and Sparta, both of whom executed the ambassadors. With Athens still defiant, and Sparta now effectively at war with him, Darius ordered a further military campaign for the following year.
The second campaign, in 490 BC, was under the command of Datis and Artaphernes. The expedition headed first to the island Naxos, which it captured and burnt. It then island-hopped between the rest of the Cycladic Islands, annexing each into the Persian empire. Reaching Greece, the expedition landed at Eretria, which it besieged, and after a brief time, captured. Eretria was razed and its citizens enslaved. Finally, the task force headed to Attica, landing at Marathon, en route for Athens. There, it was met by a smaller Athenian army, which nevertheless proceeded to win a remarkable victory at the Battle of Marathon.
This defeat prevented the successful conclusion of the campaign, and the task force returned to Asia. Nevertheless, the expedition had fulfilled most of its aims, punishing Naxos and Eretria, and bringing much of the Aegean under Persian rule. The unfinished business from this campaign led Darius to prepare for a much larger invasion of Greece, to firmly subjugate it, and to punish Athens and Sparta. However, internal strife within the empire delayed this expedition, and Darius then died of old age. It was thus left to his son Xerxes I to lead the second Persian invasion of Greece, beginning in 480 BC.'