The fact is, we don't know for sure if Alexander the Great did untie the Gordian Knot in this manner. The Knot was made of cornelwood cord and tied a yoke to a wagon; and there are 2 versions of the incident in the ancient sources: the first you mentioned (striking it with his sword to cut it loose), and the second one, according to which the King pulled out the pin of the wagon-pole, which was a wooden peg driven righ through it, holding the cord together, and having done this he drew out the yoke from the wagon pole. Not even the most accurate of his biographers -Arrian of Nicomedia- is 100 percent sure which account is the correct one, although he seems to have favoured the latter account because it was recorded by an eyewitness of Alexander's campaigns.