Arthurian Chronicles: Roman de Brut. Wace

How then shall I suffer my daughter's lord to die such a death! Rather let us hold him to ransom, and take freely of his cities and walled places, in return for his life." They, therefore, slew not the king but binding him fast with fetters of iron, kept him close in bonds for so long a space that he swore to render them all that they would. In quittance of his ransom, and to come forth from prison, Vortigern granted Sussex, Essex, and Middlesex to Hengist as his fief, besides that earldom of Kent which he had held before. To remember this foul treason, knives were long hight seax amongst the English, but names alter as the world moves on, and men recall no more the meaning of the past. In the beginning the word was used to rebuke the treason that was done. When the story of the seax was forgotten, men spoke again of their knives, and gave no further thought to the shame of their forefathers.

      When Vortigern was a naked man he fled beyond the Severn, and passing deeply into Wales, dwelt there, taking counsel with his friends. He caused his wise clerks and magicians to be summoned, inquiring of them in what fashion he should maintain his right, and what they would counsel him to do, were he assailed of a mightier than himself. This he asked because he feared greatly the two brothers of Constant, who were yet living, and knew not how to keep him from their hate. These sorcerers bade him to build so mighty a tower, that never at any time might it be taken by force, nor beaten down by any engine devised by the wit of man. When this strong castle was furnished and made ready, he should shut himself within, and abide secure from the malice of his foes. This pleased the king, who searched throughout the land to make choice of a fitting place to raise so strong a keep. Such a place he met, altogether according to his mind, on mount Erir. [1] He brought masons together, the best that might be found, and set them to the work as quickly as they were able. The masons began to build, getting stones ready and making them fast with mortar, but all the work that the builders raised by day, adown it fell to the ground by night. They laboured therefore with the more diligence, but the higher they builded the tower the greater was its fall, to the very foundations they had digged. So it chanced for many days, till not one stone remained upon another. When the king knew this marvel, and perceived that his travail came in nowise to an end, he took counsel of his wizards. "By my faith," said he, "I wonder sorely what may be amiss with my tower, since the earth will not endure it. Search and inquire the reason of this thing; and how these foundations shall be made sure."