The Greeks who were stationed at Artemisium were informed of these matters by beacons from Sciathus. They were frightened by this and accordingly changed their anchorage from Artemisium to Chalcis, proposing to guard the Euripus and leaving watchmen on the heights of Euboea. Three of the ten barbarian ships ran aground on the reef called the Ant, which lies between Sciathus and Magnesia. The barbarians then brought a pillar of stone and set it on the reef, and when their course was plain before them, the whole fleet set forth and sailed from Therma, eleven days after the king had marched from there. It was Pammon of Scyros who showed them where in the strait the reef lay. After sailing along all day, the foreign fleet reached Sepias in Magnesia and the beach between the town of Casthanaea and the Sepiad headland.