Darius, after rewarding Mandrocles, crossed over to Europe; he had told the Ionians to sail into the Pontus as far as the Ister river, and when they got to the Ister, to wait there for him, bridging the river meanwhile; for the fleet was led by Ionians and Aeolians and men of the Hellespont. So the fleet passed between the Dark Rocks and sailed straight for the Ister and, after a two days' voyage up the river from the sea, set about bridging the narrow channel of the river where its various mouths separate. But Darius, passing over the Bosporus on the floating bridge of ships, journeyed through Thrace to the sources of the Tearus river, where he camped for three days.