Darius found this advice good, and promised to reward its giver after his return. He then took a cord and tied sixty knots in it. This he left with the Ionians. "Take this cord," he said. "Untie one of the knots in it each day after my advance from the Danube into Scythia. Remain here and guard the bridge until you shall have untied all the knots; but if by that time I shall not have returned, then depart and sail home." Such were the methods of counting which then prevailed. And the knowledge of geography was not more advanced. Darius had it in view to march round the Black Sea and return to Persia along its eastern side,--with the wild idea that sixty days would suffice for this great march. Fortunately for him, as the story goes, the Ionians did not obey orders, but remained on guard after the knots were all untied. Then, to their surprise, Scythians instead of Persians appeared. These told the Ionians that the Persian army was in the greatest distress, was retreating with all speed, and that its escape from utter ruin depended on the safety of the bridge. They urged the Greeks to break the bridge and retire. If they should do so the Persians would all be destroyed, and Ionia would regain its freedom. This was wise advice. Had it been taken it might have saved Greece from the danger of Persian invasion. The Ionians were at first in favor of it, and Miltiades, one of their leaders, and afterwards one of the heroes of Greek history, warmly advised that it should be done. But Histiaeus, the despot of Miletus, advised the other Ionian princes that they would lose their power if their countries became free, since the Persians alone supported them, while the people everywhere were against them. They determined, therefore, to maintain the bridge. But, to rid themselves of the Scythians, they pretended to take their advice, and destroyed the bridge for the length of a bow-shot from the northern shore of the stream. The Scythians, thinking that they now had their enemies at their mercy, departed in search of their foes. That night the Persian army, in a state of the greatest distress and privation, reached the Danube, the Scythians having missed them and failed to check their march. To the horror of Darius and his starving and terror-stricken men, the bridge, in the darkness, appeared to be gone. An Egyptian herald, with a voice like a trumpet, was ordered to call for Histiaeus, the Milesian. He did so, an answer came through the darkness, and the hopes of the fleeing king were restored. The bridge was speedily made complete again, and the Persian army hastily crossed, reaching the opposite bank before the Scythians, who had lost their track, reappeared in pursuit.