The king was astonished at his words, but commanded the magicians to come and sit down before Merlin, who cried to them—
"Because ye know not what it is that hinders the foundation of the castle, ye have advised my blood for a cement to it, as if that would avail; but tell me now rather what there is below that ground, for something there is surely underneath that will not suffer the tower to stand?"
The wizards at these words began to fear, and made no answer. Then said Merlin to the king—
"I pray, Lord, that workmen may be ordered to dig deep down into the ground till they shall come to a great pool of water."
This then was done, and the pool discovered far beneath the surface of the ground.
Then, turning again to the magicians, Merlin said, "Tell me now, false sycophants, what there is underneath that pool?"—but they were silent. Then said he to the king, "Command this pool to be drained, and at the bottom shall be found two dragons, great and huge, which now are sleeping, but which at night awake and fight and tear each other. At their great struggle all the ground shakes and trembles, and so casts down thy towers, which, therefore, never yet could find secure foundations."
The king was amazed at these words, but commanded the pool to be forthwith drained; and surely at the bottom of it did they presently discover the two dragons, fast asleep, as Merlin had declared.
But Vortigern sat upon the brink of the pool till night to see what else would happen.
Then those two dragons, one of which was white, the other red, rose up and came near one another, and began a sore fight, and cast forth fire with their breath. But the white dragon had the advantage, and chased the other to the end of the lake. And he, for grief at his flight, turned back upon his foe, and renewed the combat, and forced him to retire in turn. But in the end the red dragon was worsted, and the white dragon disappeared no man knew where.
When their battle was done, the king desired Merlin to tell him what it meant. Whereat he, bursting into tears, cried out this prophecy, which first foretold the coming of King Arthur.