From: Early British Kingdoms

Vortigern escaped to set up a stronghold in the west. He chose to build a castle on the southern slopes of Yr Aran, above Beddgelert (Gwynedd). Construction began. However, every morning the previous day's work was found demolished. Vortigern's magicians told him to seek a boy with no father, born of the fairies. He would be able to solve the High-King's problem. Vortigern's men searched far and wide and discovered such a boy at what was soon to become Caer-Fyrddin (Carmarthen). His name was Myrddin Emrys, or "Merlin" for short. Merlin revealed that at night the mountain shook so that all buildings collapsed, because beneath it were buried two fighting dragons. One white representing the Saxons and one red representing the British, and the white one was winning! Afraid of such an omen, Vortigern fled.