In 492 B.C. the Persian army and fleet, led by Mardonius, crossed the Hellespont, in order to restore Persian rule in Thrace and Macedonia. Some have suggested that the expedition's aim was to punish Athens and Eretria for the help they had given to the Ionian Revolt. However, the Persian fleet was wrecked in a storm off Athos, and Mardonius was forced to return. Having secured the obedience of the tribes of Thrace and the king of Macedonia, he now built the bridgehead that would allow him to carry out subsequent operations against the Hellenes.

After Athens and Sparta had refused to submit to the Great King, the Persian fleet, under Datis and Artaphernes, occupied the Cyclades and launched an attack on Eretria. In the sequel, with Hippias the ex-tyrant of Athens showing the way, it landed at Marathon, the intention being to advance on Athens through the Mesogeia. The tyrant was confident that the local Diacrii would give him their support, as they had given it to his father when the latter returned from exile. But the Athenians hastened to face them on the plain of Marathon.

Strategically speaking, though the plain of Marathon was favourable to the Persian cavalry, it at the same time allowed the Athenian phalanx to develop, and this eventually gave the Hellenes victory. After the Persians' opening onslaught, the Athenian centre initially gave ground. But the Hellene wings encircled the centre and reversed the negative course of the battle. Putting up stiff resistance, the Persians retreated towards the shore and went aboard their ships, which the Hellenes bid fair to set on fire. Despite their losses, the Persians made for Phalerum, their aim being to land before the Athenians could get back. But Miltiades was able to reach Athens first, by set of sun, and deploy his army on Phalerum plain; and the Persian fleet withdrew.