Retold in our own words from the Historia Brittonum (tr. J. A. Giles) · Published 30 October 2026
The tower that kept vanishing
Literature In the Historia Brittonum, King Vortigern tries to build a citadel in the mountains of north Wales, but all the building materials vanish in a single night, three times over. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
Literature His wise men tell him he must find a child born without a father, put him to death and sprinkle his blood on the ground. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
Literature Messengers find a boy who is teased by another boy at a ball game for having no father, and bring him to the king. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
What was under the ground
Literature The boy asks the wise men what lies under the ground. They cannot say. He tells them to dig, and they find a pool, two vases, a folded tent, and in the tent two sleeping serpents, one white and one red. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
Literature The serpents fight. The white one is winning at first, but the red one recovers and drives it out. The boy explains that the red is the dragon of Vortigern’s people and the white is the dragon of the newcomers who hold much of Britain. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
Literature The same book tells how the boy Ambrose explained why King Vortigern’s tower kept falling: two serpents, one red and one white, fought beneath it. The red stood for the Britons, the white for the Saxons. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
From Ambrose to Merlin
Literature Geoffrey turns Ambrose into ‘Ambrose Merlin’, who explains the fight of the two dragons and makes prophecies. Geoffrey of Monmouth, History of the Kings of Britain, in Six Old English Chronicles (ed. J. A. Giles), Project Gutenberg ↗
Literature Britannica links Merlin with an earlier Welsh figure called Myrddin. Britannica: Merlin ↗
Literature In Robert de Boron’s tradition Merlin’s love for the Lady of the Lake leads to his downfall. Britannica: Merlin ↗
The place
Literature A note in this 19th-century translation says the place meant is supposed to be Dinas Emrys, ‘the fortress of Ambrosius’. Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
History Museum Wales lists Dinas Emrys in Snowdonia among places linked with Ambrosius, Vortigern and Merlin. Museum Wales: Who was King Arthur? ↗
History Many places in Wales have Arthurian links, though few can be shown to go back to the Middle Ages. Museum Wales: Who was King Arthur? ↗
Follow the thread
Nennius (attrib.), Historia Brittonum (tr. J. A. Giles), Project Gutenberg ↗
Museum Wales: Who was King Arthur? ↗
Retellings are in our own words. Every sentence above carries a label (History, Literature or Tradition) and a link to the source it was checked against. A medieval story is not a historical finding.
Source method & more reading ↗