"Turn him to any cause of policy, The Gordia knot of it he will unloose, Familiar as his garter

Alexander cutting the Gordian knot by Andre Castaigne

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The Gordian Knot is a legend associated with Alexander the Great. It is often used as a metaphor for an intractable problem, solved by a bold stroke.

At one time the Phrygians were without a legitimate king. An oracle at Telmissus (the ancient capital of Phrygia) decreed that the next man to enter the city driving an ox-cart should become their king. This man was a poor peasant, Gordias, who drove into town on his ox-cart. He was declared king by the priests. This had been predicted in a second way by a sign of the gods, when an eagle had landed on that ox-cart. In gratitude, his son Midas dedicated the ox-cart to the Phrygian god Sabazios (whom the Greeks identified with Zeus) and either tied it to a post or tied its shaft with an intricate knot of cornel (Cornus mas) bark. The ox-cart still stood in the palace of the former kings of Phrygia at Gordium in the fourth century BC when Alexander arrived, at which point Phrygia had been reduced to a satrapy, or province, of the Persian Empire.

In 333 BC, while wintering at Gordium, Alexander the Great attempted to untie the knot. When he could find no end to the knot, to unbind it, he sliced it in half with a stroke of his sword, producing the required ends (the so-called "Alexandrian solution"). Once Alexander had sliced the knot with a sword-stroke, his biographers claimed in retrospect that an oracle further prophesied that the one to untie the knot would become the king of Asia.
Plutarch disputes the claim that Alexander sliced the knot with his sword, and relates that according to Aristobulus, Alexander pulled the knot out of its pole pin rather than cutting it. Either way, Alexander did go on to conquer Asia as far as the Indus and the Oxus, fulfilling the prophecy.