Tell your men to dig here.  If I am wrong, execute me.  If I am right, I accuse your astrologers of ignorance.”  The king, puzzled by what the boy said, ordered his workmen to dig.  Soon they had uncovered two large, flat stones, and when at last these were removed, with great effort, they saw two dragons of colossal size, one white and one blood-red.  As soon as the dragons saw each other, they attacked one another, beginning a battle that lasted all day.  At nightfall the white dragon, though visibly tired, vomited out such a bright jet of flames that the red dragon was totally consumed by the heat and was burnt to ashes.  Then the white dragon died as well.

Young Merlin spoke to King Vortigern: "Sire, under the spot you chose for your tower there live two dragons, one white and one red, in two subterranean chambers. As soon as they feel the weight of your tower, the dragons shake themselves and the tower collapses."

Merlin told the king that he could now start building his tower without fear of its collapsing again.  The king was grateful, but asked: “Tell me, young sage, what is the reason for the dragons being locked up there, and why did they fight?”  Merlin answered the king with a question: “If your majesty wishes an answer, will you swear that I will come to no harm by telling you?”  The king swore a solemn oath that he would spare Merlin’s life, whatever he said.  Then Merlin spoke: “It has pleased God to show you a sign so as to warn you of the future.  The red dragon represents yourself, the white dragon is Uter Pendragon, who is not dead.  God warns you that if you continue to resist the only surviving son of the last rightful king of Britain, you will be burnt alive.”

Vortigern was deeply disturbed upon hearing this.  He kept his word and let Merlin go, but he also prepared for battle against Uter Pendragon.  That was a miscalculation: It is impossible to act against the will of God.  Uter Pendragon landed near Winchester, and at once thousands of men gathered around him out of dissatisfaction with Vortigern’s tyranny.  Behind Uter’s banners they marched against Vortigern, who could not stand his ground but fled north, taking refuge in an old castle.  As soon as the new king’s men arrived, they set fire to the castle.  Vortigern was burnt to death, as Merlin had predicted.

Merlin retired to the great forest that covered most of Northumberland in those days.  King Uter Pendragon wanted to make Merlin his chief counselor, so he sent messengers to find him.