The Greek towns of Thrace thought themselves rid of him, and rose in revolt; but he left 80,000 men in Europe who, at first under Megabyzos, and then under Otanes, reduced them to subjection one after another, and even obliged Amyntas I., the King of Macedonia, to become a tributary of the empire. The expedition had not only failed to secure the submission of the Scythians, but apparently provoked reprisals on their part, and several of their bands penetrated ere long into the Chersonnesus. It nevertheless was not without solid result, for it showed that Darius, even if he could not succeed in subjugating the savage Danubian tribes, had but little to fear from them; it also secured for him a fresh province, that of Thrace, and, by the possession of Macedonia, brought his frontier into contact with Northern Greece. The overland route, in any case the more satisfactory of the two, was now in the hands of the invader. Revolutions at Athens prevented him from setting out on his expedition as soon as he had anticipated. Hippias had been overthrown in 510, and having taken refuge at Sigoum, was seeking on all sides for some one to avenge him against his fellow-citizens. The satrap of Sardes, Arta-phernes, declined at first to listen to him, for he hoped that the Athenians themselves would appeal to him, without his being obliged to have recourse to their former tyrant. As a matter of fact, they sent him an embassy, and begged his help against the Spartans. He promised it on condition that they would yield the traditional homage of earth and water, and their delegates complied with his demand, though on their return to Athens they were disowned by the citizens (508). Artaphernes, disappointed in this direction, now entered into communications with Hippias, and such close relations soon existed between the two that the Athenians showed signs of uneasiness. Two years later they again despatched fresh deputies to Sardes to beg the satrap not to espouse the cause of their former ruler. For a reply the satrap summoned them to recall the exiles, and, on their refusing (506),* their city became thenceforward the ostensible objective of the Persian army and fleet. The partisans of Hippias within the town were both numerous and active; it was expected that they would rise and hand over the city as soon as their chief should land on a point of territory with a force sufficient to intimidate the opposing faction. Athens in the hands of Hippias, would mean Athens in the hands of the Persians, and Greece accessible to the Persian hordes at all times by the shortest route. Darius therefore prepared to make the attempt, and in order to guard against any mishap, he caused all the countries that he was about to attack to be explored beforehand. Spies attached to his service were sent to scour the coasts of the Peloponnesus and take note of all its features, the state of its ports, the position of the islands and the fortresses; and they