Now Vortigern had been attempting to build a tower on Dinas Emrys, but whatever the workmen did one day was swallowed up the next.
Then some wise men said to Vortigern: "You must find a youth who has never had a father. You must sacrifice him and sprinkle the foundations with his blood."
So Vortigern sent men to find a boy who had never had a father and who should be brought him that they might kill him. When Vortigern's messenger reached Caernarvon, thirteen miles away from Beddgelert and the hill Dinas Emrys, they found two boys playing games and quarreling about their parentage. And one of them, Dabutius, was accusing the other, Merlin, of having no father. They took him to Vortigern.
And Vortigern said, "My magicians told me to seek out a lad who had no father, with whose blood the foundations of my building are to be sprinkled to make it stand."
"Order your magicians," answered Merlin, "to come before me and I will convict them of a lie."
It is a terrible thing to be convicted of a lie, and of course the magicians did not wish to come. But King Vortigern made them come and ordered them to sit down before Merlin.
Merlin spoke to them after this manner: "Because you are ignorant what it is that hinders the foundations of the tower, you have told the King to kill me and to cement the stones with my blood. But tell me now, what is there under the foundations that will not suffer it to stand?"
To this they gave no answer, for they were frightened.
Then said Merlin, "I entreat your Majesty would command your workmen to dig into the ground, and you will find a pond which causes the foundations to sink."
This the King had done, and a pond was found there.