By the subjugation of Byzantium and the Thracian Chersonesus, Darius was not merely master of the whole of the important trade of the Greek cities of Asia Minor, and the cantons of Hellas, with the north shore of the Black Sea, but the path into Europe was in his hand. According to Ctesias, he bade Ariamnes, his satrap in Cappadocia, sail to Scythia and there make prisoners. Ariamnes carried out the command with thirty penteconters, and brought back captives.[253] If the statement is correct, it must refer to an investigation of the north coast of the Black Sea, similar to that made by Darius of the east on the Indus (p. 260), and at a later time of the coasts of Hellas and Magna Graecia.[254] Darius contemplated a great expedition; he wished to cross the straits with a large force, but not to pass to the west against Macedonia and the cantons of the Greeks, but to the north beyond the Danube. It must have seemed more important to him to secure himself in the north first; the conquest of the west he regarded as less urgent, and also as a less important undertaking. Herodotus tells us that Darius' object was to avenge the incursion which the Scythians made, at the time of Cyaxares, into Media.[255] It is his manner to connect events by a nexus of guilt and punishment; Darius cared very little for the disaster which had fallen on Media. We shall be more correct in ascribing to him the intention of getting the whole shore of the Black Sea into his power, in order that he might reduce the western and northern coasts, when, the south-west, as far as the Caucasus, being already subjugated, the whole sea would be a Persian lake. On the northern edge lay a district fertile in corn, and flourishing colonies of the Greeks. With this territory and these cities the Persian kingdom would have gained the mouth of the rivers of the north, and the outlet of the trading roads to the nations of the north, as it had already got command of the trading roads which met from the east and west in Colchis. But what really happened to the north of the Danube, so far as we can fix the incidents, does not agree with this plan. The object of the enterprise, unless we assume that Darius only wished to carry his arms to the most remote nations, cannot be made clear, nor can we follow with certainty all the phases in it.