But, on the insistent advice of Miltiades, the Greeks advanced to meet the Persians, leaving the shelter of their walls behind them. It may not seem to some that Miltiades made any invention in planning the campaign which he urged against much resistance, and which the Athenians finally carried out. Yet his mental action was one allied to that of making an invention; for his mind conceived a plan as a purely mental picture, then developed into a workable project, and then presented it as a concrete proposition. Later, when the hostile forces met on the low plain of Marathon, Miltiades rejected the obvious plan that an uninventive mind would have adopted. Instead of it, he invented the plan of weakening his center, strengthening his flanks, and departing from the usual custom of advancing slowly against the enemy, in favor of advancing on the run. The plan (invention) worked perfectly. The unsuspecting Persians broke through the center and pursued the fleeing Athenians to a rough ground;--only to be caught between the two flanks, like a nut in a nut-cracker, and crushed to pieces. It can hardly be seriously questioned that in this plan Miltiades showed the abilities of the inventor, and in a highly brilliant and highly important way. Had he fought the battle in the obvious way, the great numerical superiority of the Persians could hardly have failed to gain the victory, despite a really considerable superiority of the Athenians in training and equipment. But the Persians were the victims of a new and unexpected kind of attack. A new weapon suddenly brought to bear on them would have had a similar effect. This is the first illustration in recorded history of the influence of invention on the deciding of a war. Its influence was enormous in this case; for the battle of Marathon was one of the most decisive and one of the most important battles ever fought. If it had been decided contrariwise, Grecian civilization would have been stamped out, or so completely stifled that it would never have risen to the heights it afterwards attained; freedom of thought and government would have been smothered, and the world would be immeasurably different now from what it really is. The defeat of the Persians was so decisive that they withdrew to their own country, but with the determination of returning, and in overwhelming force. By reason of a variety of circumstances, including the death of the king, the invasion did not take place until ten years later. Then, in the year 480 B. C., King Xerxes set out on a punitive expedition against Greece with an enormous military and naval force.