Darius was now at liberty to take vengeance upon the Athenians. He appointed Mardonius to succeed Artaphernes as satrap in western Asia, and he placed under his command a large armament, with injunctions to bring to Susa those Athenians and Eretrians who had insulted the authority of the Great King. Mardonius, after crossing the Hellespont, commenced his march through Thrace and Macedonia, subduing, as he went along, the tribes which had not yet submitted to the Persian power. He ordered the fleet to double the promontory of Mount Athos, and join the land forces at the head of the gulf of Therma; but one of the hurricanes which frequently blow off this dangerous coast overtook the Persian fleet, destroyed 300 vessels and drowned or dashed upon the rocks 20,000 men. Meantime the land forces of Mardonius had suffered so much from an attack made upon them by a Thracian tribe, that he could not proceed farther. He led his army back across the Hellespont, and returned to the Persian court covered with shame and grief (B.C. 492). The failure of this expedition did not shake the resolution of Darius. He began to make preparations for another attempt on a still larger scale, and meantime sent heralds to most of the Grecian states to demand from each earth and water as the symbol of submission. Such terror had the Persians inspired by their recent conquest of Ionia, that a large number of the Grecian cities at once complied with the demand; but the Athenians cast the herald into a deep pit, and the Spartans threw him into a well bidding him take earth and water from thence. In the spring of B.C. 490 a large army and fleet were assembled in Cilicia, and the command was given to Datis, a Median, and Artaphernes, son of the satrap of Sardis of that name. Warned by the recent disaster of Mardonius in doubling the promontory of Mount Athos, they resolved to sail straight across the AEgean to Euboea, subduing on their way the Cyclades. These islands yielded a ready submission; and it was not till Datis and Artaphernes reached Euboea that they encountered any resistance. Eretria defended itself gallantly for six days, and repulsed the Persians with loss; but on the seventh the gates were opened to the besiegers by the treachery of two of its leading citizens. The city was razed to the ground, and the inhabitants were put in chains. From Eretria the Persians crossed over to Attica, and landed on the ever memorable plain of Marathon, a spot which had been pointed out to them by the despot Hippias, who accompanied the army.