The siege of Carystus (490 BC) was an early Persian victory in the campaign that ended at the battle of Marathon. During the Ionian Revolt the rebels had received help from Athens and from Eretria on Euboea. Darius I was determined to punish these cities for their role in the revolt. His first attempt, in 492 BC, commanded by his son-in-law Mardonius, used the land route, over the Hellespont and along the coast of Thrace, and ended after the Persian fleet was destroyed in a storm off Mt. Athos in northern Greece (Greco-Persian Wars).
Darius's second invasion came in 490 BC. This time he decided to send his army across the Aegean. A new army, commanded by Datis the Mede and Artaphrenes son of Artaphernes, a nephew of Darius, mustered in Cilicia, where it was joined by a sizable fleet including specially built horse transport. The Persian force moved west to Samos, then crossed the Aegean via Icaria, Naxos and Delos.
Their next destination after Delos was Carystus, at the eastern end of Euboea. The Persian demanded that the Carystians should supply troops for the upcoming campaign, and hand over hostages.
The Carystians turned down the Persian demands. Datis and Artaphrenes laid siege to Carystus, and devastated the surrounding areas. This convinced the Carystians to surrender, and they were forced to accept Persian supremacy.
The Persians then sailed around the coast of Euboea, heading towards Eretria, where they won their second victory of the campaign. From Eretria they crossed to Attica, landing at Marathon, where they famously suffered a heavy defeat that forced them to abandon the campaign.